I actually had 2 bad TPS's with my EZ. The one it came with ran fine for several months, then I started getting TPS errors that would occur primarily on start up, and would typically clear. It caused drivability problems even without the code present. Sometimes the code would come back while driving. FAST sent a replacement, popped it in, problems went away....for about a month or 2, then the drivabilty slowly got a bit worse until TPS errors came back.
Ended up replacing it with a Delphi replacement from NAPA, been fine since. Could be a bad batch, or the supplier of the part. Could just be luck of the draw too.