Your Welcome Kelly, glad to help. Your mechanic, thank God, knows his business

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Since he ruled out dented/bent/dirty driveshaft and balance issues, I'd have him/her concentrate on cross meember to frame nuts and bolts as well as transmission bushings and bolts. Driveshaft U-joint to pinion flange bolts, etc. Soooo many bolts and nuts.. Help!
Good luck again. I'm ready to finish some light needed mods on my bad boy and then I think I'll trade him up to a GT or a Mach 1 if I can. None of the dealers in my area have a Mach 1 available. BUMMER! Things are not staying around the dealership that's for sure. Saw a couple Saleens today in the mid $50,000 - $72,000 range. Hmmm little spendy for my budget. Plus, I'd just stare at the engine thinking.."I'm not a Special Vehicle Team, how does this darn thing work again?" LOL
Again, sometimes it is the beauty of the beast. 100,000 is about the time for our dawg's "early" transmission and suspension issues to start rearing their ugly head.
Again, glad to help. Jenn