I've had my '87 GN for 12 years. I used to get 18-22 mpg, city and highway. For the last year or so, I've gotten 10-12 mpg. Basically stock, cold air, TT93 chip, LS-1 MAF/Translator from Full Throttle, set at zero and zero, per specs., Walbro pump w/ hot wire, vacuum brakes. Car runs well, no...