pissed off about gears

[gray87GT]

After worked I stopped off at two tranny places. First said he would install gears for $1000+, second said I would need a new carrier so it would be about the same. Are these guys full of sh*t? Do you guys think it's worth it to buy a used rear end with the gears in there already, how many miles is too many??? How about rear discs.....if I got a used rear end I might as well get it with discs...so all I would need is a new master and proportioning valve right?? Any help is great cause I am stuck. Thanks

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87 GT, BBK shorty's, offroad H-pipe, ASP pullies, 70mm T.B., Cobra intake, no smog pump, Windsor Jr irons, Comp cams 1.6 rollers, F303 cam, H.D. export W.P., Tri-Ax, FMS subframes, Battle boxes, SSM liftbars, FMS King Cobra clutch, mass-air conversion, 73mm C&L, 24lb injectors, BBK fuel pressure regulator, 3/8" no EGR spacer, and other piddly sh*t.