I have a 2003 GMC 2500hd 4x4 with 6.0 and 4l80e. I was having trouble with my transmission unlocking the torque converter at 75mph. I took it to the GM garage and the tech drove it with the scanner hooked up and said that the cam sensor and crank sensor was out of time and reset the pcm. Well that cured the problem of my torque converter unlocking at 75 but then it started to unlock and lock continuously under load pulling hills. It doesnt matter whether the truck is in 3rd or 4th. It seems to start doing it above 2000 rpms. I took it back to the GM garage and then the tech said it was either a pressure switch in the transmission or the torque converter. I bought the presure switch from GM and installed and no change. Then I purchased a torque converter and installed and again no change but the torque converter seemed to help the problem but not cure it. I've also installed a new speed sensor and a TCC solenoid and again no change. The Truck has 128000 miles and I replaced the plugs and plug wires at 100,000. I used acdelco plugs and crane fire wires. I had a friend hook his live data scanner up to it and its miss firing on several cylinders above 2000 rpm's but it is not tripping any codes. I checked the fuel pressure and its within GM's parameters. Could this be my transmission trouble kicking my torque converter out? If so whats causing the miss fires? If its the cam sensor and crank sensor again whats causing them to get out of time? Any help would be greatly appreciated!!!! My friend is having similar trouble with a 1500hd 6.0 and 4l80e but its not affecting his transmission. He too had his truck at the Gm garage and told him the same thing that the cam sensor and crank sensor was out of time causing his random miss fires.