Really need some help. Been trying many things to fix a WOT issue on my truck and nothing seems to help. Getting very frustrating.
Truck is an 86 GMC swb. 5.3/4L60E. Engine has headers. Trans has corvette servo. That's it.
I can drive the truck all day long no issues. But whenever I give it full throttle it will be all good and pulling up until about 4-5,000 rpm, then all the power just cuts out and trans dosen't shift. Also the problem is intermittent. Sometimes it will do full throttle pulls great and shift great, but most time not. I've also noticed the problem may be due to heat. The times I can get it to go WOT and shift good, I've only been driving for 5-10 minutes. But every single time I take a 30 minute drive down to the drag strip and try to get a run in, the problem happens.
So far I've tried many things on hptuners(setting things back to stock, changing shift points), new tps, new fuel pressure regulator, put fuel pressure gauge on the rail(getting 58psi @ idle), new spark plugs and wires, tested for vacuum leaks.
I'm having a hard time thinking of what else it could be.
Only thing I'm thinking is maybe the fuel pump gets hot and weak after driving for a while. It is an in-tank Spectra Sp1115 and many LS swap guys use them in these trucks up to 500hp.
I've attached my tune and a data log of when the problem happens. (first spike in the graph is burnout, second one is the run/problem happening). I'd really appreciate if someone could look at these and give me some advice.
Thanks