Has anyone had Fuel Injector problems?

When I first bought my 2005 in Aug. '05, it would only avg 39 MPG for a long time. Then I read about things getting better after 5,000 and again at 20,000 or similar..anyway, I took it to my dealer every 5k for the oil/tire deal. I still was only getting about 43MPG tops SOOOO at 15,000 miles I popped for the $99.95 Fuel Econ/Performance pakcage deal which has as part of it to clean the Fuel injectors...WELL they found a bad one and replaced it!! The computer did NOT show any codes..no lights on the dash flashing or anything!! Soon thereafter I was topping 54MPG on a trip into the Hill Country of Texas with 3 adults and a full load of lugauge !! About 3 tanks fulls ago (1 month?) the milage dropped down to 41MPG and the best I have had of late is last Sunday on a 600 mile journey of 47.6 for a short time. BTW, My wife and I agree that the only screen to use to tell how the car is really doing is the overall 30 min (every-five-minute) one. The others vary so much during a tank as to be NONE useful. I just had it in the shop before this last trip due to the low MPG and they said they got 57MPG in a 4 mile test curciut....useing the energy screen...I got up to 98MPG useing that one this last trip !! BUT, it changes every second..SO WHAT !!??

Sorry to rattle on...anyone else ??