Poor gas mileage and no low end power
 

So my 97 legacy gt has been running pretty crappy lately. Between 2k and 3k RPMs I have no power. The car is currently only getting 15 mpg as well. The stuff I already did were NGK wires, new bpt, all new silicone vacuum lines, new intake gaskets. I am running a 2.5" custom cat-back with a knocked out cat and aftermarket header. Any help would be appriciated.

Glad you asked this...I'm getting nearly that too and i do not enjoy it, I know I need a front cat and o2 replaced. Hopefully you get skme help here

Have you done a fuel filter or fuel system cleaning?

I did do fuel filter and just changed fuel pump too. I also just had my cel pop up with the o2 sensor code so I guess that is the next step

I am tackling those next...headers, front car and front o2. I hope they help a little but how bad are gas prices up there? Have you tried injector cleaner?

Prices are 3.50 here and I've used a couple different injector cleaners and some water removers

sounds like O2 to me. same thing happened in my truck, mileage dropped from 16.5 to 7.5 mpg and it ran rough. changed that O2 out and all good in the hood.

you running an intake?
go back to stock and the mpg's will increase