I've got a 92 3500 4 door dually 4x4. 454 tbi with a 4l80e trans, I'm not sure what gears though. Plenty of power but not so good mileage. I get 10mpg towing or empty give or take. Thought maybe someday to upgrade to a newer diesel of the same truck but have seen that even the newer diesels only advertise 11mpg towing. Doesnt seem like much increase for the cost of the truck. So my question is, for less money than a newer truck, what can I do to this truck to increase mpg even by a little bit? Has stock single exhaust no cat with a larger muffler (cant remember brand) engine pretty much stock.