I just did a tune up on my 4.3, Plugs, wires, cap, rotor, pvc, serpentine belt and fuel filter, runs like a dream except for one little problem. When I pull out from a dead stop, it runs through first very normal, shifts into second, if I give it more gas here, nothing until 5 or more seconds later, then it picks up, shifts into third fine. There are no other problems with her that I notice. Transmission was rebuilt about 5 years ago. Any ideas where to look first ?

 

If there are no codes, I would check fuel pressure then do a live data stream to see what the computer is doing.

Search random+hesitation and see if that sounds familiar