Bucking/Hesitation/Stalling after driving on highway
Someone PLEASE help me out here.
I have a 1966 GTO with a 455 built by Don Johnson at DCI Automotive in Ohio. The engine has an aggressive cam, and is currently putting out 440 HP at the rear wheels. Don is great and no complaints on the motor.
Here is my issue, after driving the car on the highway for 25-30 miles, and when I go to pull off the highway and let off the gas, the car wants to die. I can keep it from stalling by keeping on the gas but you can all imagine the fancy footwork going on as I'm in town, with a 4 speed, trying to stay on the gas so it doesn't die while braking with my left foot. When this happens, it also gets worse under load, so when I put it in first, even though I'm keeping it at 2,000 ish RPM, it hesitates and is bogging out. If I get it up to 3,000 ish RPM its better but can still tell its running very rough.
It seems to be worse in the summer when its hot, but not exclusive to summer. Also not exclusive to highway driving. It can happen after driving it stop and go for awhile and it heats up. This was happening with the motor at about 190 deg. I'm noting this because I was thinking is this vapor lock? (I have mechanical fuel pump).
It started last summer when I was on the highway and it would start to die even on the highway when I wasn't exiting and letting off the gas. It wants to die.
I have had 2 different large carbs on here and it sthe same with both. My mechanic in Philly (muscle/classic car specialist JD's Performance) thought it might be an electical issue and put a "filter" on it. Didn't fix it.
Can someone help with some ideas here please!!! Its so frustrating I don't want to take the car anywhere as I'm worried about getting stranded (or worse causing a traffic back up).