Gearing is too high by a margin. With GT12 cars you need to be at about 40deg of timing max and around 65/68mm/rev. The timing and gearing you have is why you are getting max speed at the end of the straight.
Because of the weight of a GT12 car gearing needs to be lower. At the weight you have it needs to be even lower! Talking of which I now don't understand why you are so far overweight. Please gives us the information Mark asked for so we can have another look.
Good to hear that the car is now handling better and some effort has been made to stop hitting things!
Your 'difference' still suggest some *cough* variation in the driving department from lap to lap, but as you now have control of the car, that will come.
Whilst looking for more speed and less weight, focus on the consistency in every race. Just because you don't have the speed you need is no reason for hurling the car around - every race is a chance to get consistent.
The late, great Phil Davies when he first appeared on the scene was racing at Watford one time. He consistently hit the same corner lap after lap. I remarked to someone else that once he sorted that out he would be great. Multiple British and European Championships duly followed! Get consistent, then get fast.
Looking forward to the details requested so we can comment further.
