I am currently running LT285/75R16 on the stock aluminum rims that I too switched to from the stock steel wheels. I have 3.73 gears and with the oversized tire I switched out my vssb to one from a truck with 3.42 and my speedo is within 1mph according to a gps. I tow a 25' 5th wheel with a truck and trailer combined weight of 13,500lbs... tows great just have to watch the egt's on the uphill on warmer days...
1995 GMC 2500LD,6.5L TD,Ext cab, SB,4L80E,3.73,Heath Chip, Turbomaster,Hayden fan clutch, 3\" exhaust,K&N filter,Aux Fuel tank, High Idle,Remote Start,Homemade headlight booster,2 inch suspension lift,285/75r16 wrangler at/s. p_holmen@hotmail.com