Tldr: rebuilt right side (passenger) cylinder head, installed solid lash adjusters, replaced several plug connections, new spark plugs, new ignition coils. Still misfire on number 8.

2002 Dodge Dakota SLT 4.7 2wd manual transmission. Engine replaced at 150k chassis miles by previous owner. Currently at 206k chassis miles.
Replaced hydraulic lash adjusters with solid lash adjusters, messed it up, and turned right cylinder head into a paper weight.
Got doner head from junkyard jeep commander, stripped, cleaned, lapped valves, torqued everything to spec like a paranoid person. Followed Haynes manual ritualistically. Went back together smooth.
As I waited for gasket maker (timing cover) thread lock (solid lash adjusters) thread sealant and anti seize compound to set, I cleaned the fuel injectors in several bathes in ultrasonic cleaner. Flushed them and replaced o-rings. New spark plugs with .038 gap. Replaced several broken and or dry-rotted connections. I used original wires with new plug where I could, else I spliced with the "glue inside" shrink tube butt connectors for permanent water tight seal.

Fluids added, rotated engine to bring the fresh motor oil to valve train, then start up. Sounded like a v8 running on 5 cylinders. Found two ignition coils that didn't change the engine when unplugged. Swapped ignition coils from cylinder 1 and 3 to 6 and 8. Engine sounds like 6 cylinders running. Replaced the suspected ignition coils. Now only sounds like one cylinder misfire. Cleaned all connections and it runs smooth until I lug or work the engine at running temperature. The misfire shows most when hauling weight at capacity: 1000Lbs, driving up a steep hill in too high a gear, or charging a dead battery vie jumper cables at 1500 rpm.
Pulled the spark plug and it looked a little more like a cold spark/carbon fouling plug than a new plug after 2000 miles since rebuild. Cleaned, checked gap, replaces. Swapped ignition coils between #6 and #8. Still misfire on #8.
I'm honestly thinking it's the fuel injector, or electrical gremlin in the harness. I can pull it apart and replace wiring. But that's a LOT incase I'm missing something obvious. I'll pull the valve cover in the am to check for ejection of rocker arm (I highly doubt this is the case. I used a .015" feeler Guage to set the tolerances on the solid lash adjusters. Tight enough I could pull the feeler Guage, but couldn't put back between the rocker arm bearing and cam.) I checked other threads about misfires, and the directions lead to no progress.
What do you think?

 

Swap injectors between six and eight. See what happens.

 

Alright, swapped injectors between cylinder 6 and 8. Put everything back together, cleared the DCT code and idled the engine occasionally revving to 4000rpm to aid in warm up and use more of the ECU's mapping. After about 8 minutes the rpm floated between 800-1500 without my inputs for two minutes. Once it settled, my obd2 reader threw the cylinder 8 misfire code.

 

Rent some noid lights. Verify you are getting good steady signal to the coil, and injector. Begins to sound like an electrical problem there..... Maybe failing PCM?

 

Looks like harbor freight has a kit for 30$ online. Probably 45 in-store. I can take a trip across town and pick that up. If the computer is failing, could I send it to a place to reprogram or is it hardware? I wanted to get the Diablo tuner, but if it's failing, should I look into mega squirt or speeduino? I was considering those options anyway, but that is a LOT of work.

 

Its more likely a hardware issue. Bad solder joints, or something similar. There are places that will repair them, if they can, or sell you a reman unit, but, most of 'em have really horrible reviews, and chances of getting a "Good" replacement, just ain't that great. Still and all, cheaper the a couple grand or so for some other standalone system.