fuel problem with my 76 grand prix need help

I have a 1976 Grand Prix,,455 automatic,with a 650 holley carb.car runs great at idle and even if you stump on the gas,but if you run it up to 3 grand and hold it there,it acts like its running out of fuel,and it stumbles on take off,have changed pump and filter,has a clear filter and it stays full of fuel,while the car is acting up,,any idea's would be great..maybe its not fuel,I just dont know at this point,,, changed plugs,has tayler wires I dont think they would be bad,,car set for 10 years,before I got it...had the carb cleaned,with new acc. pump and power valve..

oh yeah how the hell do I get the distributor lose cant get it to move either way...

There's a vacccum advance that extends out from the lower part of the Distributor....check it and see it that's where Your problem lies?

Ok....the distributor is bolted/locked down with a forked shaped piece of metal that has a 1/2 inch or 9/16 bolt,it's located right at the base of the distributor shaft and is a PIA to get to.They actually make a funky little tool to loosen the bolt,it's a 2 piece tool that's L-shaped on both ends and it comes apart,it has a 1/2 socket opening on one end and the 9/16 on the other depending on the bolt size You need to loosen.

On a side note...You may need to spray a little WD-40 to loosen the bolt for the distributor hold down and don't over loosen it because the distributor with be able to spin or move too much or too easily.