I picked one up for my 4.8 the other day for 150 bucks. I currently have it set on the 87 tune, what kind of number increase from that alone should I see? is it worth swapping out to the premium fuel and do that tune? Should i select 20" under tire size if i have those size wheels? im pretty clueless when it comes to tuners and things of that nature and id love to maximize the effect of a handheld tuner.