Here's as detailed a history as I can think of for background, specific questions at the end.

1998 2x4 Ram 2500 manual trans - former load hauler company fleet vehicle bought used at 198k miles, now with 215k. appears to have been well maintained and retired due to worn out suspension. (name brands on emissions parts)

First problem was a slowly clogging converter misdiagnosed as faulty fuel pump...
in AZ summer heat (a year ago) something under the hood was intermittently shutting down fuel pump, which I attributed to the MSD6A I had just installed WITHOUT the 8910 tach adapter and got occaisional error codes (no CEL) that research determined was typical of installation without the adapter (not enough signal to computer to drive fuel injection) so... I reverted to stock til I could get around to the 8910 as well as eliminate possible cause for fuel pump shutdown. Weather was cooling down so no extreme heat to test it, everything seemed to be operating problem free.

Converter failure progressed, (no CEL or codes) ran increasingly like a vehicle losing the fuel pump and/or clogged fuel filter, pump would still shut down in extreme heat, (engine not overheating) and start/run normally when dead cold, just no power beyond low rpms. Seemed a safe assumption that pump/filter was the issue... fuel sender was causing problems too. Turned out to be the converter when it was apparent it still wouldn't rev up with new fuel pump. Converter failure confirmed by removing primary o2 sender and having full power. Replaced cat and truck had more power than ever before...

Problem seemed solved... MSD reconnected with 8910 adapter, truck ran great... for a while... until replacement pump failed, (verified dead with separate power source) as well as the fuel level sender... (I hear something knocking around in the tank so suspect the float arm came off.) I suspect pump is just foreign made POS since I made budget constrained mistake of buying cheap replacement on fleabay.

Not having time to drop the tank and put the old functional pump back in, I used the auxilary fuel pickup on the pump housing and installed a 60psi external pump as temporary solution... back on the road! for a while... noted that once in a while was not getting enough fuel on acceleration coming off idle, was not getting any OBD codes os figured low quality filter was contributing cause (stumble and occaisional backfire starting from total stop, typical of accelerator pump not working properly on a carbed engine)

then again in the hottest part of summer (this year) things went really haywire... on the way home one hot night after helping a friend move, the ignition cut out dead as I was cruising down the road, CEL came on, now what??? Since it had previously had problems I had wired the MSD such that I could quickly switch back to OEM for redundant backup... 10 minutes later back on the road, CEL off, but could tell engine wasn't quite right with what i could call slight misfire or timing issue. So I assumed it was heat again and 5 miles later stopped somewhere convenient for 4+ hours to let it cool off. Fired right up, ran great... for 1/4 mile then cut out again, but NO CEL this time.... quick roadside test confirmed pump functional but no spark, ended up needing a tow home. Still no spark once engine was cold, though have cleared the OBD codes after reading with tester but not yet disconnected battery.

OBD came back with plenty of error codes:
p0171 - mixture too lean (obviously related to auxilary fuel pump and acceleration stumble, or perhaps not changing the primary o2 sensor when cat was replaced)
p0351 Ignition primary failure (no spark,duh) same code as MSD occaisionally generated without the tach adapter the very first time the fuel pump cut out.
p0463 fuel level sender failure (I knew that, had been running with out it working for months with no code)

Onboard monitor test indicates test 11 and 15 failure (had not appeared any time prior to this no spark failure)
On board monitor test codes tough to locate but found a comprehensive listing of on board monitor test codes here:
https://dodgeforum.com/forum/1516881-post6.html
CODE 11 - Timing belt skipped 1 tooth or more from initial learned value, Intermittent loss of either camshaft or crankshaft position sensor, No crank reference signal detected during engine cranking (I suspect crank sensor as primary culprit)
CODE 15 No vehicle speed sensor signal (where/what is that? did not see on electrical schematics I found or references to same elsewhere)

other misc details: did not change out the primary o2 sender, noticed that new stainless steel cat pipe turning colors with heat, first blue now brownish/blue, new to stainless exhaust so not sure if this is normal.
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Questions and primary issue being short of funds this month, would appreciate input for a get it right first time solution, have not yet picked up a factory service manual. Also have concern that ECM may be failing due to being an AZ vehicle all it's life, heat being known contributor to premature electronics failure, all my problems occured on days over 100 degrees and even hotter at street level. FWIW it's over 150 under the hood in the sun with engine "dead cold," no small wonder the paint bakes off the hood.

I have searched all forums found CODE 11 related to CRANK sensor (per Intrepid forum comments,) Code 15 would seem related to crank sender as well. Please confirm and/or comment.

Need confirmation that the key dance for 1998 Ram 2500 generates no codes/flashing, just a instrument panel check, which shows all good.

Anyone know if any of the above P OBD codes would also disable the ignition spark? Fuel pump does come when engine is cranked.

Lastly is there a simple way to eliminate ECM as source of troubles? I suppose I could use some electronic parts testing chiller spray to cool it fast otherwise not found simple diagnostics if any such exist.

Thanks in advance for your help.

 

First thing to check is the plenum gasket. This will contribute to so many other issues, such as cat failure, misfires, and cracked heads.

Did you relpace the cat? How about O2 sensors>

 

p0351 is no power to the coil. This code in addition to the code 11 makes it sound like a bad crank sensor or faulty wiring.
Make sure wires are routed per this TSB http://www.dodgeram.info/tsb/1998/18...8-48-98-v8.htm

The lean condition and drive-ability issues are most likely attributed to a blown plenum aka intake manifold vacuum leak. The cat and O2s are failing because of the blown plenum -- Read the stickied thread on here "end all be all plenum thread"

Buying a quality fuel pump assembly (fuel pump, sending unit, "filter") like Denso or Delphi...and not any other brand, will fix that code and any other drive-ability problems.

The speed sensor is the sensor on top of the rear diff.

 

Will look into the plenum issue, truck was running great except when ignition cut out.
Cat was replaced, o2's not, appears they are functioning as the truck passed AZ smog check a few months later at the very bottom of the range with *******ly no emissions. Got so much power back after the cat was replaced took me two days to stop chirping the tires... mileage increased to 20mpg +/- with MSD and K&N

Will read up on the plenum issue, hoping it was dealt with previously with near 200K on it, the cat was the factory original so no surprise there, caught it by chance saw platinum flakes in a dirty oil drain pan that happened to be sitting off the side of the truck. The factory cat has a much tighter grid than the replacement, never mind no longer obstructed, no wonder both power and mileage went up, until it crapped out was as much fun as my long ago 383 cuda.

Will check into wiring as I've had packrats cause issues before, the speed sensor now that you reminded me was my own fault, misplaced the screw that holds the ebrake cable bracket onto the axle tube during aborted attempt to install traction bars and later saw it had shifted over and was rubbing on the wires, simply forgot about it.

Thanks to both for your input. Might take a while to check everything but will post what I find/fix when I do.