When was the last time you did a tune up on that thing? Could be as simple as a messed up wire or plug not getting spark into #1 which means no burn which means wet plug and way less power.
2000 Mustang GT Steeda #0048 34k miles. 99 Cobra 4V swapped, FTBR IRS swapped, exhaust, tuned by James Gordon.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.