My t-5 is brand newly rebuilt, but could it be my rearend? my friend told me just to not downshift with a t-5? i dont want to go through this again

any opinions?
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90 lx coupe: 5spd, 177k miles, steeda water pump pulley, Mac coldair fenderwell, Mac h-pipe, supercoil, ADS chip, 160 stat, aluminum D/S, Black magic fan, 3.27grs.
Best time: 13.9116(on 225/60/15 firehawks)
Best mph: 98.17
Best 60': 1.9607
next mods:4.10's, slicks.