Looking for some help. I have a small block 360 drag race motor. After adding aluminum heads last season, there was a small stumble if you try to jab the throttle from idle. I footbrake race, and when I bring the car into stage I'm at 2500 rpm. It has never stumbled when on track. It only happens from idle. Timing is at 36 degrees. I tried 38 as well, but no change. Primary squirter is 35. I tried both up and down and no change. Power Valves are blocked and jets are at 76. It runs as smooth as can be other than when I jab the throttle at idle. Starting to get frustrating so looking for any ideas/suggestions to try. Thank you in advance!