Hi, I normally lurk in the Classic Mustangs forum, but the engine in my '70 fastback is a 383 retrofitted with EFI. My problem is that when my engine is under moderate to heavy load, it misses, hesitates, and pings, and the tach needle jumps around. If I accelerate very gently, it runs fine. Fuel pressure is good, and the spark plugs look normal. This is only a recent development -- it has run well for nearly a year to this point. Any thoughts?