I was looking at this engine and it shows that an engine controller is required, Im assuming since you used stock wiring harness and pcm you didnt need that? Also the stock throttle pedal works or did you get a specific one?
Does the engine come with a base tune to run it?
Did you swap any parts (besides the exhaust manifold) over from the old engine to the new one or was everything available?
Finally which torque converter did you have to buy? And whats the reason for a new one?
GM performance primarily sells these motors to folks putting them in hot rods, retro rods, custom builds etc so in those cases you will need the computer. The engine controller from the 5.3L is the same one used for the 6.2L as the motors are so close. The motor came with a gas pedal but again, same one it already had in the truck. The tune that was in the PCM for the 5.3L fired up the 6.2L no problem and ran pretty good, just needed to performance tune the way I wanted. You WILL need somebody with the expensive tuning software and who is experienced and good at tuning these motors, also need to test on a dyno many times to get it right. Took about 4 days of fine tuning to get it perfect.
Here;s the official parts swap list from motor to motor:
Oil pan from 5.3 to 6.2
Exhaust heads from 5.3 to 6.2
Water pump from 5.3 to 6.2, (they were the same GPM pump but the old one had the hook ups in the right place so no more mods needed to connect)
Torque converter.
The stock TC was too (small, weak, slow?), anyway when you came to a stop the engine still pulled hard at idle. I would have to stand on the brakes at idle and it would idle down the street at about 30 MPH. With the new 3000 RPM Locking torque converter it did away with that and now drives like a stock truck. It also took about 1 second off the 0-60 times, I guess just a better hookup when you stomp on it?
