focusing on your problem, since you seem like you are out of many other options, i would take it to your local Toyota dealer to get it fully inspected. the same inspection they would give it if you bring a vehicle to them you are looking to buy. it will set you back 100 bucks or so but they would probably find whatever is causing it. despite any problems going on here between people, im sure most can agree this guy has a problem with his truck if what he is saying about conditions, driving habits, etc. are true. these inspections check EVERYTHING and it is a good option if you are completely out of ideas of what it could be. when you take it, it might be better to not mention your gas mileage issue so they dont think what people on here have already told you to do. if you do take it, post up what they found. im sure most of us would be curious to see if there is a problem.