My 99 Ml 320 runs great bu maxes out at 115mph an still seems to have plenty of throttle when I get to that piont. How can I get my ML to cruize at 120+?>>

The top speed is limited by the computer, based on the speed rating of the tires that were factory delivered on the vehicle. Look on the door frame or inside the gas cap cover for your tire specs. My guess is the cut-off is 112 MPH for your T rated tires. Or maybe 108 if they are S rated and your speedo is off.

Most aftermarket chips for performance increases remove the top speed limitation but will likely cost you $500 plus to purchase.

Regards,

Jim