i was told that my 86 had the 8.8 rearend in it but then i mentioned that it had a tag that said it had 3;73's in it and then was told it aint stock if it has those gears...so has my rearend been changed or is that normal for stock or ?

 

to my knowledge none of the 5.0 came with 3.73

but you can check, lift the rear and and mark the rear tires and driveshaft. also leave the car in gear.

 

the tag probably says 2L 73 = 2.73 gears... check it again for that config of letters/ number