I'm having an issue when cruising in my dart for somewhat long trips on the freeway. When I go over 20 miles or so, if I try to push the car it'll start to backfire and act like its not getting fuel. It makes this noise like "k-thunk, k-thunk, k-thunk, k-thunk" until I let off the throttle. The car has a pretty stock 383 with schumacher headers. The 727 has a 2200 stall. I was in an accident recently so I don't have a full exhaust system... it's cut off right after the mufflers. I don't remember having this issue prior to my accident, but there are some changes that the car has had since. The rear end now has 3.23s and a true trac instead of 2.94s. I'm also running 27" tall wheels in the back now. When I'm on the freeway, I'm usually cruising at 4000 rpm give or take. Also, my car before didn't have a hoodscoop. Quite a few new variables, but any thoughts?