New to the forums just rebuilt my 4l60e on my 2003 Silverado. I did a few upgrades to help with longevity and performance and had a few questions. Here is my issue. I have many in building performance engines but I'm definitely not an expert at transmissions I did check the functionality leak down and engagement of the clutches and diaphragms. All the clutch clearances were on the lower tight side but completely in spec.

I have a stock 2003 Silverado. I just finished rebuilding the transmission. I have only built a few auto transmissions before. I have the transgo, shift correction kit and the sonnax pump upgrades with the spring spacer the new valve the trans-go .500 heavy duty boost valve and different springs. I used the Drake performance clutch and rebuild kit for everything else. I also bought the upgraded aluminum diaphragm with the o ring and the corvette aluminum high performance super servo. and the sonnax billet overrun piston kit. I upgraded to a 5 pinion planetary gear set with the heavy duty shell. a towing lock up converter from drake. I just installed the transmission. everything shifts smoothly when in 1st 2nd or 3rd. but when I put it in drive and it shifts something is cutting power to the engine. Almost like its a traction control issue the truck is still running perfect it just cuts out, just wont go under light load. It actually works perfect if I hammer the throttle. Any help or ideas would be greatly appreciated. if I take off in 3rd it runs and shifts perfectly. Just wondering if anyone has run into an issue like this. I have no codes popping up and I do have a tec 1 computer to diagnose but I don't see anything odd in live data. Thanks for any suggestions or help. I was wondering if possibly the lock up converter is possibly locking up with too much engagement. But it looks like the computer is shutting signal down to make it only idle.
Thanks for any insight.