Exactly as the title states, lol. I have an 8.8 in my car with some vibration issues. I'm honestly sick of dealing with it. I was supposed to be picking up a 4.10 posi 8.5 last week, however while it does have 4.10 gears, its an open diff! So now I am kinda stuck. I planned to just throw it in and drive it, but I want the posi. So either I drop $400 on a 28 spline carrier then spend more later when I upgrade axles, or just jump for the 30 spline and then order axles, and get the housing cut for 9" ends. The issue is, do I want to drop that much cash into an 8.5? Is my money better spent on a quick performance 9" which already has bolt in axles, upgraded to a new center sections, ect ect for about $2500? What would I be looking at cost wise to upgrade my 8.5 to the level of the 9"? What is the difference in the power level of each rear? Which route should I go? I just want a rear that bolts in with 100% stock stuff and will hold up do some clutch dumps on slicks at the track hopefully into the 10's if I ever get there. (Right now its a high 12 second car at ~4000lbs). I'm sick of doing it over and over again too! Thanks guys!