I found that it was actually cheaper to just buy a 8.8 take off rear end and swap rear ends. It already has the Tlok in it and you can decide if you want 3.31, 3.55, or 3.73 gears by shopping for one that already has the gear set you want. I spent a lot more on the 7.5 in my 2006 installing a tlok and 3.73's than it cost me to put the 8.8 in after I broke the 7.5 at the track on a tune, CAI and drag radials.
And the tlok is not made any longer so you have to look at other options (make sure that they are 28 spline) and if the 7.5 tlok ever needs to be rebuilt you are out of luck. No one makes a rebuild kit for one unlike the 8.8