wanting a tuner for my LLY that will get atleast alittle better MPG in city driving, and can change tire sizes????

HP Tuners can give you better mileage if you keep your foot out of it (just like any other programmer.). It will change your tire size for the speedo, but if you don't know how to adjust the "tune" to achieve the better economy then this tuner is probably not for you. It requires a laptop computer to run the tuning program, and also load the tune to your truck. Some of the vendors on here will write tunes for you, and this is nice because you have all kinds of options for future mods. with a "hand held" programmer that has pre-written tunes you are stuck with only those tunes. That may work better for you, PPE has a great tuner for that application. But if you want to spend the money for a good quality tune, look up duramaxtuner.com and Nick can help you with EFI Live (EFI Live is pretty similar to HP Tuners). There may be a vendor on here that does HP Tuners, and Nick may even do them as well. Hope this helps.

-David