I did my mods with FI in mind...hehe...and it had 4.10's in it when I bought it. The guy who bought it new put on the 4.10 gears along with extra overload springs and trailer brakes. It sat a little higher than stock in back, which is the reason for the 2" leveling shackles. It surprises me that the previous owner who went to all the trouble by putting in the gears and stuff--why didn't he put in posi also???? I haven't broken down the tranny yet, so I am not sure if it has a shift kit from the previous owner. When we dropped the tranny to put in the TC, the fluid was 100% perfectly clean at 70k miles. But there is one weak link to the drivetrain---the POS G80 rearend. That thing sucks!!!! Whenever it looses traction, the G80 chunks and bangs around...I WILL be doing a Tru-Trac soon...