loosing power/backfire through carb

OK I did a couple of diagnostic tests and here are the results; compression is on average about 110 in each cylinder with less than a 10 psi difference between the highest and the lowest readings. Vacuum test on carb showed slight fluctuation at idle no more than 1 inch. At 2000rpm vaccuum was constant. On releasing the the throttle (letting of the gas) the vaccum maxed the gauge and then returned to orignal idle reading. I get hesitation at start and around 35-40 mph and occasionally a backfire through the carb when lettign of the gas. Only when letting of the gas quickly do I get a bakfire through the carb. However it is inonsitent sometimes it happens somtimes not, but when it does its only when realseing the throttle quickly. The hesitation is kind of a ru-ruum thing that is much more consistant than the backfire. Does this help? How about you guys tell me what test to do and I can post the results.

again the engine is a 273 was a 2 barrel stock but now,doug headers,
old holley street dominator manifold, eddy 500cfm carb, mopar electronic ingnition, msd coil, doug headers, xtreme energy comp cam 250 (800-4800rpm), bored over .020 whole thing rebuilt with about 40 or 50 thousand miles on it.