If you left the transmission in overdrive, that's what did it. When you get into a hill that causes speed loss, manually shift out of overdrive.

 

That's messed up, so it's always going to do that?

 

Fixing the plenum, cat, and timing chain and gears will take care of most of it.

 

Well, yeah, pretty much. However, the more power your engine is capable of at the relatively low engine speed during overdrive operation, the steeper the hill you'll be able to climb without losing speed. 'Scuse me while I get nerdy here (and assume that my calculations were for the converter clutch engaged mode of operation, too):

Suppose you're running a stock truck with 245's on it, so your effective tire radius is 14.25" and the circumference is then 89.54" -- for every full revolution of the tire, the truck moves 89.54". If you're in third gear with a 1:1 ratio from crankshaft to propeller shaft, and 3.55:1 differential gears, you'll get 3.55 crankshaft revolutions for every tire revolution, so 1.775 combustion cycles per tire revolution.

Shift into overdrive so your crankshaftt-to-propeller shaft ratio becomes 0.69:1, and now you're getting only 2.45 crankshaft revolutions per tire revolution. That's 31% fewer combustion cycles per tire revolution -- 1.225 combustion cycles per tire revolution. In third gear you were getting ignition every 50.4 inches of forward travel, in overdrive it's one every 73 inches. Or, to view it another way, you dropped from 1257 pops per mile to 868 pops per mile. Or, to make it easy, your engine RPM at 60MPH dropped from 2514 to 1736. These engines make relatively very little power at 1700RPM.

To make it directly applicable: At 75MPH your crankshaft RPM dropped from 3142 to 2168. A stock 5.9l Magnum makes about 50 or so fewer WOT horsepower at the lower speed than at the higher one, and when you point that combination at a hill those fifty absent horsepower make their absence known.

Just poke the silly button to make the OD Off light come on when you're going uphill. Nuthin' to it but to do it.

 

Well that makes sense I've just never noticed it on any other trucks I've driven..

Looks like I'll be doing some work to her. About to start a build thread, excited!

 

Also, keep in mind, that with the bed plenum, possibly plugged up cat, and a stretched out timing chain, you are not making even close to what the engine put out new..... Changing the timing set in my truck was THE BEST thing I have done to it. MAJOR change in how the engine runs.

 

I see in your dig you have a double roller timing set what brand did you go with? I was going to look some.

Also if I create a new post and upload pictures I tried to upload 10 different ones but after I clicked upload only two showed up a pgn one and jpg will all of them be there? Btw I'm on an iPhone doing this

 

Agreed! After the tune up my truck feels so light on its feet, gets up to 75 on any on-ramp easily.

@Just curious - I would just do all the tune up at once, only a couple hundred dollars worth of parts and a weekends worth of work. Tear it all the way down the timing chain and also replace the oil pump, screen, and gasket.

 

I have read several threads where this is mentioned. "Great improvement" or "engine runs better" but no one has ever gotten more specific. I mean, put a muffler on and we get detailed dyno runs and "seat of the pants" and "holy cow" descriptions of results. I'm just wondering what EXACTLY a new timing chain does. My truck runs the same as it ever has (over 15 yrs) except I'm chasing a weird vibration that I hope is the clutch. My other thought is timing chain but it is a HUGE job. As big as plenum which I had a shop do. I'm a weekend greaser/oiler and the chain scares me a bit. Just wondering how dire it is and what are REAL results because I've also read of these engines going to 300k with stock everything.

 

As the chain stretches, cam timing is affected. Basically it gets more retarded (as in, valve events occur later, not that they are getting stupid....) as time goes by. Which effectively moves your power band HIGHER in the RPM range. Exactly what you DON'T want in a truck.