After a major tune up on 93 Camry, new plugs, wires, injectors, etc. It runs good some of the time, but after full tank of gas, it burned the heck out of the gas, 50 miles of driving and the tank was half empty, then it like changed and got good gas mileage, probably 175-200 miles on the rest of the tank. Filled up the tank and it happened again. Any ideas what could be wrong in the tank? any help would be appreciated.