I love how people just change the computer when they can't figure things out

First off only the center wire should have a 5v reference on the TPS. It shouldn't even be 5 volts it should be about 4.6 at WOT, at idle around .65-1.25 volts. One of the other two wires should have a straight power and the third should be a ground, I believe. Best bet would be to get a wiring diagram of the computer find which one is supposed to be the 5v reference/memory and which one is supposed to be the straight hot lead for the computer first to make sure that isn't crossed. I can't remember the wiring off-hand though

Another thing to note, computers usually only run the grounds in cars as a standard. If you have a hot wire going to a ground, going to the computer, you could definately cause some beautiful things. As far as the bad gas mileage, the car is probably in "limp home" mode meaning it's running full rich because it can't see what the throttle position is at. If you need to I can print out a computer wiring diagram from ALLMOST Data (hehe) and scan it, then send it to you. Just give me the Exact year model etc. Or what year/model the engine is, if it came from another car.
Another note, did you guys check out all the fuses before hardwiring in the computer wire? I know it sounds stupid but you'd be surprised how many of the guys in my school over look that and look into it being something bigger, then they can't figure it out. Come to me whining because I'm the electrical guy, I go over replace the ECU fuse and get back to what I was doing