Keep in mind, the engine tune is picky with the weather changes. When the temps drop, the air becomes more dense, and you will be too lean. to combat this, as it gets cooler out, you will need to richen your mixture. The humidity will greatly affect your tune as well. The best bet, is to re-set to the factory settings, and re-tune.

As for the 2.5 being a 2 gallon engine, that is not true. I know of a few people, who got 5 or more out of it. I was going on my 4th gallon when I sold mine, and still running STRONG.... anyone here can back me up on the way my 2.5 ran.

Take your time, be patient, and don't be affraid to ask for help. I'm sure there is LOTS of life left in your engine.