I have an '89 5.0 5-speed Mustang GT. Before I go further, I did have a similar post out here a while back. Please stay with me though. During full throttle acceleration in first gear it starts stumbling well before red line ... by 3,500 or 4,000. It's like it runs out of gas. Yet it's fine at part throttle (just did this today) right up to 5,000ish with no problem. It's fine in second gear at full throttle all the way up to 5,000 and beyond. It only stumbles at full throttle in first gear.
The fuel filter and fuel pump have been replaced. I've checked for codes. I've checked the TPS. I have no clues. It runs perfect except at full throttle in first.
Ideas anyone?
Thanks very much! Dave