'88 Trans Am with a TPI 305 and auto tranny with exactly 80k miles. I blew my 2.73 posi differential the other day and I need a new rear-end, but I've been considering putting a shift kit in it as well. I've been looking on eBay and they have $76 kits and $36 kits. Is there a difference between the two kits, or just who is selling them? There's a few people selling at each price. Was curious as to what the benefits are of one over the other.

Also, I'm planning on doing this myself, and it would be my first time. Is there anything else that's cheap and worthwhile to replace while I have the pan off? I've heard of people using an upgraded servo and boost valves, etc. Is the boost valve included in the shift kits? I don't want to do a full rebuild of the trans though.

My car will have either 3.23, 3.42, or 3.73 posi gears in it behind the trans and the motor should be putting out 260HP or so by the end of this summer, and my plan is to drop in a 355 putting out 400HP over the winter (not sure that's going to happen that soon anymore, but MAYBE)..

Also, are there any true benefits from upgrading the separator plate to the $16 ones that are on eBay?