Thank youI don't know if this will help, but here is a tune I built in about 10 minutes.
Initial final gear 5.300
Top speed 118
First gear 2.750
Second gear 1.750
Third gear 1.340
Fourth gear 1.080
Fifth gear 0.900
Sixth gear 0.779
Final gear 4.700
If it doesn't help, can you try to describe what is going on?
Edit: I don't know what a decent time is but I was able to lap the track in 53.5s with my bad driving style.