Take the TFI off and take it to the parts store and have them test it. They need to run the test multiple times to generate enough heat to simulate driving conditions - they fail due to heat, so if it doesn't get hot, it may not be an accurate test.
2006 GT - Vortech polished w/ intercooler, Eibach suspension, Hurst short-throw, some other goodies - tuned by Paul's High Performance. It moves...
SOLD - 1995 Black Mustang GT, AODE. Loved it, but I had to let it go...