I traded some work at a ford dealership and im thinking about having them change my gears, but want to make sure i have them do everything i can while they got it open and apart. Since day one when my Grandpa bought the mustang (now mine) it had a rear chatter not sure why he never took it back for warranty, a buddy at ford thought it was a the rear clutch pack, it will chatter at a really low rpm and when im at about 30mph and then like 70ish mph, if i put it in 2nd when im doing like 20-40 i never get the chatter. When i was getting some work done at a shop they told me about an additive and while they were working on it i had them add some and it didn't fix anything they said it may need more but you cant add too much.. Anyone else ever have this problem? And what else should i replace while its all apart? And what are your guys takes on adding the Ford Racing aluminum rear differential cover Will it fit mine without modding stuff or are there better ones? What about these Ford Racing Rear Gear Super Install and/or Rear Axle Bearing & Seal Kit? And im thinking about 4.10s, Wondering how bad it is on the freeway doing 80mph or more? (I don't drive a lot on the freeways to really care about saving gas but im curious about it) Car Info: 97 GT Auto Thanks!