I stand by Dura Lube fuel system cleaner every 3000 or every 6000, just before an oil change.
It has been getting harder to find, and I stopped using it for a while, to see what would happen. Even with only top tier gas, and a bottle of techron cleaner every now and then, the Trac got to a point where it was starting to lose something, mileage, performance... I had forgotten about the dura lube additive.
One day I saw it at Strauss, poured in a bottle, and everything was back to normal. It almost works instantly.
I've used it across 2 vehicles now and love it. I had tried it years ago in a blind test on a friend's car. He was complaining about hesitation and how loud and rough his engine was running, he did not believe in this sort of stuff. I convinced him to add a bottle while the engine was running, on the "give it a shot, what have you got to lose" premise. He poured it in, and we were both amazed as the engine suddenly quieted down and the rough idle smoothed out. I never had that issue, and I thought he'd need to drive a bit for it to work.
However, there is no substitute for diligent and proper maintenance. TBI cleaning should be done yearly, plugs and wires checked / replaced periodically, some form of in-tank injector cleaner should be used periodically, oil changes with oil and air filters replaced / cleaned religiously, especially in very dirty areas (NYC). My air filter is guaranteed to need a cleaning every 3-6 months.
With the warmer weather, I was pleaseantly surprised to achieve 22MPG at 65MPH across 2 fillups, on the GSP from NYC to Atlantic City. I was forced to 65 because I had a wheel out of balance (feels awful).