You killed 3rd gear. Either the speed gear or cluster. Libery makes a 9310 gear set that might live longer if you refrain from operatibg the car in the manner stated above.

Spinning hard and dead hooking it on the upshift will do that. Much like rolling a mechanical diode in a 727.

What clutch is in the car and how much does it weigh? You need something that slips a bit on WOT engagement.