p0300 & maybe the transmission

[Axis]

So I'm trying to diagnose a problem with my truck and I'm running out of ideas... there may be a couple problems. I'm hoping you guys can help. I recently finished swapping a 2001 6.0/4L80e/t-case into my 1995 z71. Truck ran great for a few days, through a few heat cycles, and I put about 65mi on it before the problem started. Now it seems to be way down on power. It'll fire up no problems, and if I put it in gear it'll pull itself out of the garage (level ground). But if I give it gas, it hesitates and doesn't want to accelerate. The driveway has a slight incline and if I stop, and let off the brake the truck will intermittently roll backwards--it'll sit for a few seconds, roll back, catch itself, & repeat. If I drive it around, it almost acts like there's something dragging in the driveline that the engine is trying to overpower. As it gets warmed up, it starts to act like the trans is in Neutral where the RPMs increase, but it doesn't accelerate. If I'm careful about how much gas I give it, it'll hold and accelerate.

The truck rolls free with either the trans or t-case in Neutral. The transfer case shifts freely and the problem exists in all t-case gears, but it's less noticeable in 4Lo. Problems exists in all trans gears, but a 2nd gear start seems to be worst as far as not wanting to move. The 2500 driveshaft was shortened with new u-joints. I had to redo the rear brakes & wheel cylinders after the problem started, so I can confirm the e-brake is not hung up. Consequently, I don't think anything in the driveline is bound. I changed fluid/filter and installed a Transgo shift kit during the swap. I changed the fluid/filter again after the problem started & didn't see any significant metal or debris in the pan.

At a loss, I checked dtc's and pulled a p0300. During the swap, I converted to a 1998 fuel tank and installed a new fuel pump and filter. Hooking up a gauge, pressure at the rail is good & doesn't bleed off. The pressure regulator (not new) seems to test good. Injector wiring has been double-checked and noid lights show all injectors getting trigger signal. A stethoscope sounds like all are cycling. Fuel (91 octane) came from a heavily used gas station and had 50+mi on the tank before problems.

The swap got new ACDelco plugs & wires. Plug gap was checked before install. Coils have PWR & GND. A spark tester shows all plugs to be firing. I pulled plugs for inspection, and all looked about the same & in good shape.

I haven't been able to find a vacuum leak using either smoke or propane.

I tried disconnecting upstream O2s. The truck threw a p0300 when cold, and the problem got worse when it warmed up (but was still in open loop w/ no O2s). I have confirmed that upstream O2s are wired correctly Bank1 to 1, 2 to 2. The truck has cats. Rear O2s are functional and not throwing any codes.

Engine was rebuilt during the swap, and got rebuilt 799 heads with a small cam. So I don't expect it's compression related. EGR was eliminated. Tuning was done by a reputable tuner in the truck community (and ran good for 65mi). Harness was done by me with all connections soldered and shrink-wrapped. I don't have easy access to an advanced scanner without taking it to a shop, but do have an Autozone loaner tool scanner. I'm trying to diagnose this without throwing unnecessary parts at it, but I'm running out of ideas.

[farmtruc]

Starting with the misfire.
No access to a scanner is gonna make it tough, determining which cylinder has the misfire will make it a lot easier. When an aftermarket cam is installed, the misfire window needs to be increased (maxed out) so that the pcm doesn't detect.
Of course this disables the misfire counts.
Does it feel like it's an engine hesitation lack of power issue , or something binding in the trans that is keeping the truck from accelerating?

[Axis]

It definitely feels like a trans issue. That's what prompted the diagnosis: it felt like it was eating the transmission when I drove it. When I couldn't find what was wrong there, I tried pulling codes and found the p0300. The misfire does throw a code, but hasn't tripped the SES lights.

I took it out this afternoon for 20min or so. The forward gears seemed to improve significantly. The 1-2 shift isn't near as firm as it was before the problem--it used to almost bark the tires. And if I give it more than about 30% throttle, it makes a strange noise at about 20mph, kind of a metal on metal whine. I took a video and will try to get it uploaded. When I got back to the house, Reverse seemed to be badly binding. I had to stall it to over 1000rpm to get it to roll backwards down a hill (idle is about 675rpm), and it actually rocks a little when you let off the gas, like its unloading something. Neutral does not roll free, and acts similarly to Reverse but as a forward gear... if I give it gas in Neutral, the truck moves forward. 1st gear and all the other forward gears still move it forward also, but they aren't binding nearly as bad as R or N.