@O5BIRD yes. I advise playing first with the throttleResponse. I haven't thoroughly tested that yet, and would like to see if people actually find it adequate for the task. Input for the funky trees solution is basically Pitch+PitchAngle/x A bit more complex if you want it to add power when also climbing in reverse and not add power when you're going downhill.

@O5BIRD you can edit the acceleration in a number of ways. One is a funky trees input that increases power as the pitchAngle increases, while having very low power on flat ground. It lets you climb slopes while being slow and cumbersome on flat ground. Another option is brand new. It came with 1.11 update, and is, in my opinion, a lot handier than funky trees. Add a line throttleResponse to the engine in Overload, and adjust a number. It will tell the engine how quickly to throttle up. Default value is 1.
I usually tweak my suspensions until they are nice and cushiony. Try running your vehicle over some rough ground and see what feels good.
Another thing is steering. Default steering of wheels is far too quick, and I advise always using rotators to turn the wheels. That way, you can adjust the rotation speed, so it feels like someone inside is actually turning the steering wheel.
I hope this helps.

Credit to @scratch