I have a fairly stock, CA emission 95 GT convertible, 5.0. I have made the following changes: MAC cold air tube, BBK 70mm TB, MAC underdrive pulleys (the MAC products were problematic but that's another story); 9mm Ford spark plugs, rotor, cap and fuel filter tune up.

When I first installed these items I could definately feel a difference (more horsepower) when driving the car; however, after a few months I've noticed that the car doesn't feel like its pulling as strong as it use to on the upper end AND when I try to restart the vehicle once its warm it starts hard and sometimes even coughs or backfires. It sort of feels like a flooded carburated motor. I had a mechanic hook it up to a code machine and run it at idle and he said it was running lean. These doesn't sound right, even though I saw the meter and the reading. It is just feeling like its flooded. What should I do?

Oh, I have run a couple containers of Red Line injector cleaner through several tanks of gas. The car runs great on this stuff with the octane enhancer (made for autos with cats), but once that tank of gas is gone its back to the same scenario.....

This sounds like a problem we had wit hmy 85 LX, it had an EFI 5.0 that was mostly stock except for exhaust, ram-air, and headers. It would have good days and bad days, on the bad days it would studder and stumble while under a load, but at idle and cruising it would be pretty fine. We were planning on installing a high performance motor in it anyways so we did it sooner and the problem was solved, we still don't really now what was wrong with that engine, except that it had a lot of carbon on the pistons was about the worst thing.

If i were you i would put a smaller thottle body on. Like 60mm or a 65mm. It is getting too much air. Or you could try putting bigger injectors on to even up the fuel to air ratio.