Built trans first. I put a 4400 stall in my stock trans and it started slipping bad after my first time out. I have the stock rear and am cutting the times and 60' in my sig still no problem. Now if you had an M6 I would deff do the rear first. But auto's have a lot more cusion on the rear cause they always have pressure on the gears, they dont have that shock from dumping the clutch.

 

i say trans too, autos' are soft on rears. stick with slicks though if possible, dr's are more likely to break ****.