Hmm try modifying
(artificially make acceleration slower, but same top speed).
gear_1st = to higher number? Say 4
gear_2nd = 3.5
gear_3rd = 2.8
(try to reduce inertia hence reduce wheel spin?)
wheel_inertia_rear = 1 (from 1.05 of higher number)
and if all fails, this is sure 100% to work. (much more grippier rear tires hence much better rear traction, more power sent to the road to push car instead of lost in wheel spin).
grip_rear = 2
I'm at work, so can't test these values obviously. You can test though, see if it works? When getting back home I'll try too.
Cheers!