I have a 1993 Nissan SE-V6 4x4 extended cab P/U. I love it. I just put 15x8 American Racing wheels and 31x10.5 BF Goodriches on her. Even before I put these items on it, the speedometer needle started to shake back and forth when going above around 40mph at a constant rate. During acceleration, I don't notice it, just when I let off to stay at a constant rate. I can't use my cruise control, because the truck slows and speeds up as the needle does. Anyone know what the hell is going on and how much it will cost me to get it fixed?? I can't take it anymore- HELP!!!!!!