MML = Motor Mount Lift. There are two types of MML. One is taller motor mounts that completely replaces the stock mounts. The other is a budget MML which is a spacer that goes under the stock mount. The MML raises the front of the engine/transmission/transfer case assembly which reduced the angle at the drive shaft. This is a common fix for drive shaft vibration caused by suspension lifts. Another common fix is a transfer case drop which is spacers put between the frame and the skid.
At four inches of lift you have entered the range where the best fixe is a SYE, slip yoke eliminator. The SYE puts a shorter, stronger rear output shaft on the transfer case and uses a CV drive shaft.