Car acts weird?

I went into the game files for the Ishibu Miramar and tuned its 1.9 L engine to have more torque and higher rpm and rev limiter. But when I floor it, no matter the rpm, the rpms max and the speed slowly climbs, I release the gas and the rpms go to (lets say) 7000 out of 13000. The tires don't lose traction, it just barely accelerates. I don't know what's wrong. (The attachment is the newest tune, although I have tried multiple and this problem still occurs).

 

You have flat spots in the torque curve... Also, the highest amount of torque is being delivered at the highest rpm.

 

Also, how do I edit the grip of the miramar?

 

you're curve isn't a curve though isn't the issue here. You're issue is the clutch, you need to increase the clutch torque

 

How do I edit the grip of the miramar?

 

You can't, unless you change it for all vehicles. To edit the grip you would have to look pretty hard in the game files. Which isn't a smart thing to do as it can break the game.