You can run the truck decent with a MM without transmission tuning. Honestly though, I would do it at your earliest availability. H&S OD Tuning really helps with puting that power down and will greatly help to save your tranny. With tranny tuning, you can push the truck harder without worry of the tranny giving out. Granted, if you are really hard on it and get a little stupid with it, you can still toast the tranny in no time. All a matter of how you drive it.
2008 2500 6.7 6spd Auto
Carli Suspension 3.5 Dominator with triple bypass rears, Control Arms, Front Hydros, Sway and Stab. Tube Bumper, Solteks, Trussed Axle and Toyo M/T 37s