Hi everyone, long time reader, first time posting.
First, thank you to most of you for all the helpful information I have gained.
Second, my problem:
I have a 99 chevy tahoe with a new v8 5.3L engine (2k miles ago) I put in myself with all new electronic sensors, computer, coil, everything except distributor (new rotor and cap and sensor though), i have also replaced the fuel pump and filter, injectors. Nothing on the transmission.
At around 2500 rpm the engine misfires when 3/4 to full throttle but not if I ease into it. If I let the throttle up and it shifts and give a little more throttle it won't do it anymore. But if when it starts to miss and I give more throttle it almost want to stop but still persists to miss and hesitate. It does it more often when its cold and i get right onto the interstate. It has not given me any Check Engine Soon lights lately but it used to (I know that i should have got the codes read but lives are hectic sometimes)
Please help, stumped, and the mechanic is stumped. Let me know if anyone needs more info.
Thanks

 

Welcome to the forum.

Best guess is fuel starvation. Check fuel pressure. Assuming new pump is good (not a good assumption sometimes), may be the regulator.

Others here might have some more/better ideas.