If you haven't done a full tune up, do a full tune up. Assuming you have the stock heads:
-Autolite 25 Spark Plugs
-Trans and diff fluids
-Clean MAF sensor
-If you have access to 93 octane fill up with that and set timing to 14 degrees advanced
2000 Mustang GT Steeda build #48. Bolt ons, suspension, Novi 2000.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.