Tuner
 

I am looking into getting a tuner for my 2002 4.0L 4wd ranger. I saw a Jet performance programmer at summit but i've read they can cause problems and to get a xcal2. I've never done anything like this before so i want to get it right the first time. which would be better and do you have to buy codes separate or do they come programed into the tuner? I;m going to buy one new so i was hoping it already came programmed. How much more power will i get out of it and i also need it to recalibrate my speedometer cause i just put bigger tires on.
Thanks