I finally figured out why the players car is so slow in a straight line!

@ScarDuck14 Can I just check mate...do you only restart practice sessions after drag upgrades or do you restart qualifying and race sessions as well ?

Ah ok, so it's a known issue? I don't understand how they did not figure that out previously when they were making the performance patch. I actually did notice it I think around august last year, but then I stopped playing the game because I hated how the car was handling. Now I made some mods to the tyre wear and it seems to have fixed the problems I had with the car suddenly snapping on me mid race, even though it still happens sometimes. I increased the front tyre wear by 12.5 percent and also modded the rear tyres to heat up a little less by 5 percent. The car feels so much better when the tyres degrades evenly.