I'm guessing you're not running cats. Did you mess with timing/does it run smooth? Is the trans shifting into overdrive? Even running baseline it should get about 16-17 mpg. Do you have the front O2's hooked up?
Pulled the tstat, filled it, and it ran fine the first day. Second day the temp gauge fluctuates and I have intermittent heat again. It looses coolant, but I can't tell if its leaking anywhere because by that time its usually overflowing out the overflow container.