Handling modeling for Super Heavy (High Mass vehicles)

[CLT1167]

Hello everyone. I've been working on a Cop Killer M3 GTR Mod which involves a helluva lot of horsepower and even more mass (15000 killos to be exact!) 15000 is the mass value I have on the M3, I'm just trying to find sufficient values to make the vehicle drive properly. Right now, it move as you would expect a normal car to, but once up to 30-50 MPH, it flutters between 40-50 MPH and rapidly shakes. I'm unsure what's causing the speed loss, but I suspect it's the suspension and tire values. I have to find out which ones so I'm banking on somebody here knowing kind of how this works. I can provide exact values if needed.

[CLT1167]

Also to add further context, I did get the vehicle to work, but it drives like a brick on ice powered by jet engines. I had up the boost to 320PSI to make it go faster than 50 MPH