Long time owner of a 67 390 gt 4 speed fastback. It's been a very reliable runner for 20 plus years, but the past 6 or 8 months i've developed an issue which i need some input if anyone has had any similar issues. Seems in warm weather like now in the midwest, after the car has run for maybe 10 or 15 miles and is good and warm, it develops a stammer pulling out of first gear from a stop. Alternatively, it also stammers going up a hill or incline at a good speed 40 to 50 mph's while it's been up in fourth gear for an extended distance(at least a mile or two without and downshifts). The stammer, or hesitation probably a better term, is accompanied by a backfire. Initially when it started, i got the wiring around the manifold and valve covers all replaced. There was some old splicing that was in need of updating etc. Theory was when things got hot something was touching something hot. Didn't stop it. Also replaced the clutch bearing on what is a newer Ford Performance clutch as we thought possibly it was not disengaging when it gets real warm coming out of first gear. I'm not a mechanic by any means, but an old car lover like probably a lot of guys in their 50's. Does anyone have a similar experience, or does the backfire which is accompanying it mean anything to any of you old Ford veterans out there? It's odd because it 1. won't do it while the car is relatively cool( was ok in winter), and 2. the car has not to this point just shutdown. Any thoughts or ideas appreciated. Love the car, and it runs great other than this recent tough one to call. It has original wiring from the dash, etc. so i'm guessing it could be some sort of other connection issue?