I run a 3500 convertor in my daily. Drives like normal. Even bumps when put into gear with an 800RPM idle. Sounds like that EL camino had a junk convertor or other issues.
My PTC 2800 is the same. I have my idle set at 700 and it bumps when put in gear. It also moves at a pretty decent speed maybe 10 or so MPH in gear idling.
My neighbor has a ~475hp LS swapped C10 with a 3800 stall and it runs and drives like a normal vehicle.