If you have a 3.8 with auto go with the 5:13 gears for 37" tires, I have 35" and think I would like my gearing better with 37" since I sometimes tow on the hwy.
i had the ring&pinion shop out by you do the install, i now have a mechanic that could have done it for me.
at 75mph in OD about 2500 rpm and in 3rd it is at 3400 rpm, you would drop almost 200rpm with true 37" tires.
I towed a trailer to Georgia and It just could not quite hold OD and 3rd was needed with any headwind or uphill grade.
Im in Commerce MI. your just around the corner, I intend to go 37" soon and Toyo is my first choice if the extra 10lbs is not noticable to performance.
Im installing the Ripp headers tonight hopfully and will report on the results