Physics Body Vehicle Questions

Hi,
I am making a Vehicle class that utilizes Static Mesh with Physics enabled I have ran into a few minor issues I was hoping someone could point me in the right direction.

1. The Current Speed Of my Vehicle keeps on Increasing as long as I am pressing the forward button even though I apply counter force if the Current Speed Exceeds the Max Speed Limit.

ForceStrength = MaxSpeed - CurrentSpeed;

This works but still the current speed of my vehicle keeps on increasing, I suppose this is due to the physics body’s momentum but any idea how can I make the vehicle go at a constant speed? So it may not exceed the max speed limit? (I am using AddForce Function So I think this will be a bit hit or miss)

2. Physics Body Slides off or starts rotating.
So This one I was able to do by adding counter force for right vector to keep the vehicle from sliding due to physics but I have found on lower FPS this flies the vehicle off the map and jitters. Any Suggestions?