99 silverado hesitation

Hello group,

I'm in need of some ideas, my truck is as follows:

I get a hesitation when I apply small amounts of throttle, If I push the pedal down, more like half to three quarters then the hesitation goes away and the truck accelerates. Worst case is when I have a short stop, say I run into a store for smokes and a soda, (5-10) mins, the hesitation is very severe to the point that it will not rev over 2000 RPM, UNLESS I push the pedal past half throttle it feels almost like its loading up on fuel and opening the throttle clears it and it starts to accelerate normally again. Twice now when this has happened it has backfired through the exhaust, although not a very harsh backfire, but loud enough that I heard it, again thats only happened 2 times. The real kicker? This doesn't happen all the time, most of the time but not all, once in a while it runs smooth as silk.

What I've done:

R&R dist cap rotor wires plugs< 2 times, fuel filter, air filter, TPS, multiple cans of injector cleaner. also had to replace one O2 sensor (B1S2) other O2's are working fine according to scan tool.

Fuel pressure seems to be ok as after it clears and under high acceleration it runs fine. I'm considering the injectors and spider unit as a possible next step, but thats a $350 dollar part, I can install it.

So if anyone has any ideas, tips, hints, please don't "hesitate" to reply :)

Thanks to all that take the time to read this ...