Well all the V8's have a trac lok which is a limited slip differential. It uses clutches to distribute the power when one side is slipping. These clutches wear and that is why you spin both or you spin only one. Meaning it is time for a rebuild of the trac lok.
2016 VW GTI 2.0 Turbo
1989 Sonic Blue LX Coupe, 349 ci, TW heads, TFS Track Heat Intake, 75mm Accufab TB, 80mm ProM, 30 lb. inj, TKO, 3.73, 31 spline w/ TruTrac, MAC 1-5/8" LT headers w/ H pipe, Flowmaster, electric fan Moates QH
391 rwhp & 424 rwtq...Mustang Dyno 11.5@122mph