[Screwed2002]

I am not sure what the issue is with my L motor swap into my 2002 Screw. A little bit of history, Truck originally had a 4.6L with a 4R70W trans. I swapped in a complete L motor out of a 2003 Lightning (Oil Pan to Intake to Intercooler) I kept the stock ECM and wiring harness and the 4R70W trans and did a soft rebuild, shift kit, and bought a heavy duty torque converter for the trans. I had to redo some of the original wiring harness to work with the new L motor (TPS sensor wire, and IAT Sensor Wire) I had to buy another flex plate that fit on the L Motor crank, and had the correct bolt pattern for the 4R70W converter. I have an XCal II tuner, and went to a reputable tuner to make sure everything would be OK with the original ECM. I put the stock tune back on the ECM before I started any of the swap. Once the motor was in, and everything in place, I cranked the truck. It started on a dime and everything was smooth. I took the truck to the tuner to have it dyno tuned, and thats when all the issues began. I drove it there, and once on the dyno, he was trying to change some of the shift points and limiters so he could begin tuning the truck, and right as he connected the tuner for the first time, something went wrong. When he tried to start the truck, the idle was horrible, and it would barely stay running. He worked on it for hours trying to diagnose the problem. I mean I drove the truck there, he checked over everything including fuel pressure, coils, voltages and could find nothing wrong. He continued to try and return the tune to stock, and that didn't help either. So I was stuck there for a long time. After about half a day of this, mysteriously the stock tune went back in, and the truck idled and ran OK. He attributed the issue to be with the ECM, because he could never find anything else wrong, he even thought maybe it was the exhaust clogging up, because I had brand new dual exhaust with hi flow cats and magnaflow muffs, but when we disconnected the exhaust to see how it acted with open manifolds, it did the exact same thing and wouldn't idle right, and wouldn't run right when giving it gas. So in the end we kept the truck in the stock tune and it would run right, he only got it to produce 330 hp on the dyno but said it was cutting out for some reason at higher (above 3000) RPM's. The truck was driveable, and at this time I REALLY needed it since it is my daily driver. Phew this is long..... OK, now after driving the truck for a long while I noticed that the cutting out (almost sounds like its hitting a rev limiter) gets worse when the temps are hotter outside. If I get on it while the temps are less than 72 degrees or so, it screams, and the cutting out is a whole lot less, and not until higher RPM's like around 4500 to 5K RPM's. As the temps warm up, the issue is worse and starts around the 3K mark. Any ideas as to what this may be caused by? I am ready to start delving back into this issue and wanted to see if anyone else has experienced anything like this on a L motor swap. Could this be caused by one of the sensors or something. I am blind now, and want to get my truck running right......Please Help