For F1 generally, you really do have to ease into the throttle and cant just mash it once you are out of the turn. Once the car is set right with the right combination of tire, you could technically drive it very aggressively, but until then, you just have to be gentle with your throttle.
What happens when you try to apply more than 60% throttle? If the car starts wondering and very touchy to drive, esp down the straight, change the ackerman angle so they are more straight rather than angled. I had the same problem as first, but changing the ackerman instantly calmed down the car.
The stock rear tires provide very little grip on asphalt surface and recommend you use something else. The stock center spring is very short and not suited for this kit IMO. I switched to an Xray 2.8 long body shock spring and that helped handling as well.
What damper grease are you using? did you put any shims under the rear pod to increase its pivot range? what are your ride heights?