The slow rise is the fuel expanding from the warmth of your engine. Mine is all the way on zero PSI when I go out for a cold start, and I get like 28 PSI at higher rev than you list, low 30's at other spots, and I don't get those codes. Doesn't mean I'm right, just may mean that you have a different issue (maybe how much fuel at higher rpm, or loose wiring making pump cut on/off). FPR and or that 6 inch vacuum line for it (pin hole)?

 

can you humor us and see if you can find a local ECU off of a known code-free truck to test out?
maybe while youre disconnecting your ecu take some dielectric grease and glob it on the ecu connector on the harness, and maybe on the crank sensor as well (hit the vehicle speed sensor too so it doesnt gum up too)...

if it thinks its misfiring and youre not feeling anything in the cab, my guess is still something electronic, and unrelated to injection hardware...

any weird wiring harness changes to your truck - crank signal line running near battery cables, fuel injector wiring, spark plug wires, or alternator wiring?

 

Or knock sensors.... or shield of crank sensor wiring not grounded (only needs one end to be grounded)

 

Eric...2x on the wiring check.....when I first got my truck someone had "tapped" into the #1 ignition coil wiring for an aftermarket security system.....It kept giving me misfire codes until I found the wire by accident one day.....while this probably isnt your specific issue...I would recommend going through every connector you can ( again) since many of them must have been unhooked during the previous repairs....good luck

 

Ive seen a few bad alternators causing random misfire codes such as yours on gems vehicles too. Usually you can tell if you put a dome lamp on and it gets dimmer and brighter fluctuating, kind of like it's got a power surge. You can also check the AC voltage the alternator is putting out at the alternator. I think .5 (1/2) vac is the max. Still the best way to test this is with a scope.

 

Mike G brings up a good point about regulation of the power supply. When you drive long enough for this to warm up and start the zombie dance, does it continue from that point on? If it did, slipping off the serpantine belt and running on pure battery , or removing the 100 amp fuse link would remove the alternator from the equation. As mentioned earlier, could be induced noise being picked up by the cable from the CKP to the ECU (it's like a microphone cable, in a way). Some change in wiring route might change it, and it is the sort of thing that is easier to see with a scope, if you are familiar with that technology and what to expect on the screen.

 

Thanks for all the ideas guys. I've been sick but managed to get some things done with your feedback.

Cleaned reluctor tabs
Moved plug cables away from harness
Disconnected rear O2 sensors
Repaired knock sensor wiring

After multiple drive cycles the codes appeared to be gone so it seemed like it was fixed. I had a suspicion the misfire codes would return if test driven from a cold start, so this morning I took it out for a drive and bam, P1313 P1314. The pattern seems clear now. I can drive all day from a warm start, even 100 F, and no misfires codes. If I test drive it from a cold start (mid 30s lately), P1313 P1314. Hmmm...

 

ECU temp sensor new or old?

 

And on that theme, ECU ECT sensor providing realistic reading? If wiring intermit to sensor.... mine will read an engine coolant temp of -40F if unplugged. So your OBDII scanner might show what that reading is and if it (and the IAT) make sense. You can clean up connector to sensor, and I even took mine out and cleaned with a metal brush to get calcium off of it. Very little coolant loss, you are at the top of the hill so to speak.

 

Coolant temp sensor is old but has always read the values I'd expect. I've never seen the value fluctuate and I always watch both IAT and ECT on the UltraGauge.

I wonder if the fuel temp sensor could have anything to do with it. Time to RAVE...