I have a 93 SSE. Before my transmission went out the first time i was getting around 17-18 MPG with a massively slipping tranny, then after i got it back and then rebuilt the motor and i have been getting around 15 MPG and need all the opinions and ideas about waht could cause my mileage to go down so drastically. any help appreciated

Lots of times, a rebuilt engine will be a little tight for a while until the bearings and other moving parts get worn in to each other. This will affect the fuel economy. But 17mpg is pretty low for these engines. Assuming all the normal tune-up stuff (plugs, wires, filters, pcv) has been done....How old is the oxygen sensor and is it a Delco? Did you replace, or clean, check and flow balance the injectors?

Just a couple of ideas.

Yeah ive done all the tune up stuff. I haven't been able to do the injectors yet, but i was also thinking what about the fuel pump? could low pressure cause it to?

Low pressure won't cause a poor mileage problem. You're DUMPING fuel somewhere, not running low.

Check the resistance of each wire with an ohmmeter, and report the numbers back here (or bring your car over tomorrow while I'm finishing up the SSEi and use my meter). Pull at least the 3 front plugs and inspect them.

Pull all 3 coils and check them (I have a couple spares).

You better come over tomorrow around noon or so.