Which rim and tire size combo would be the best? I would like to keep the same overall demensions but with either 20's or 22's.

 

Bigger than 18" wheels will kill your ride quality (worse than it already is)

I have never had a stock drivetrain but I believe the most you can go with is a 325 height. Not positive on width, but if I had to guess I'd say around 10-11" to be conservative

 

Thanks for the info. I have to say though the ride quality is not that bad compared to my dads. I've got an 04' 2wd f-250 crew cab lariat with the 6.0 and hes got an 01' 2wd f-250 extended cab with the long bed on it and his rides like a tank