GM had settled with me after having multiple issues with a car we owned. After trading the car in for another vehicle type, GM contacted me about setting up a restitution settlement. Provided documents as asked about the payments we made to GM financial, assuming settlement check we got was a return of payments we made on account. But before GM cut us a check. I had to sign a release of claims document with a notary certification.
the way I would look at this situation is you traded in the car and got $X in trade-in value. then GM made restitution which i would regard as part of the trade in price because the defect lower its trade-in value.
now you have to look at the tax basis of the vehicle - purchase price less deprecation if any. if the trade in value including the GM money exceeds your basis you have taxable income first deprecation recapture up to the amount taken any excess is capital gain. if it was purely personal then any loss is not deductible but any gain is taxable - long-term capital gain if you owned the vehicle more than 12 months.