Get 2 of the ones that plug before the catalytic converter.
Reason they have so many is because the 96 + gt has 4 o2 sensors(2before, 2 after)/
Good luck.
Let me know if your gas mileage improves.

I m having same problem but I think mine is due to clogged Cats .

 

Wow, the Napa nearest to me sold me two 02 sensors for 80 bucks [&:], I can't imagine 70 bucks a sensor. It's better just to suck it up and pay for it though.