Not running perfect...need some help please

[BJA69C10]

So, my truck has been running really rough lately. we thought it was a timing issue, so we sent the truck to be looked at. I just got her home today (after three months ) and it still isn't right. We had a brand new HEI distributor put in, with new coil, cap, rotor, plugs, wires, etc. But the truck still seems to be miss firing. heres the symptoms:

Runs fine at idle or when reved in nuetral

Makes a popping noise under acceleration, similar to a backfire, but almost seems like it's going to stall

sometimes it clears up as the rpms rise

and lastly...it seems to run perfect imediately after a left hand turn?

Maybe the truck was meant to be a circle track racer?? I'm thinking it could be carb problems or maybe some water in the fuel tank (stock location).

I do have an Edlebrock 4bl and intake that i could put on...

Sorry for the long post, I just want to figure this out so I can get her painted =]

Thanks for all of your help guys,

Brad