I seem to have the worst luck getting gears in and reasonably quiet. 2008 4.6. Going from 4.10s to 3.55 to ready for more power. So, yesterday, I had the 3.55s installed by a VERY reputable mechanic who has done them a thousand times. I was with him to assist and learn, and he is very credible. Used the FRPP kit with carbon fiber clutch packs. Note, I already have a T56 Magnum XL with one piece driveshaft. Everything went in fine. At first attempt with shims, he got backlash to .010. However, the gear pattern wasn't to his liking. So, we removed everything, reshimmed the pinion, and got a good pattern. Rechecked backlash and reshimmed it and got to .008. Since spec is .008 to .012, we called that good. Buttoned everything up, bolts torqued to specs, and we're on our way. Pulled out . . . and the damn thing whines LIKE CRAZY on decel. It calms a little above 65MPH, but it is downright obscene from 50 to 35. Doesn't go away completely until you're at 25 MPH. The slightest tip of the throttle makes them quiet as a church mouse. We expected some noise because I have poly rear suspension parts. But, the mechanic said he has never had one sound that bad. So, we're going to try to reset it next weekend. He is ordering a new pinion bearing and crush sleeve, just in case the bearing was damaged when he pulled it back off to reshim the pinion. Also going to make sure the carrier didn't shift forward when load was put on it from not being shimmed tight enough. By the time we work on it, the gears will have about 100 miles on them, and my mechanic thinks they won't be ruined that fast if we get them set right. Any other thoughts?