Well try lowering the fluid level in the tranny first but my ranger probably has the same 4WD setup it is a 1991 when you put it into 4WD the computer that controls it should click if it doesn't than that is what is bad if not then your motor is just dirty you have to take the little 4WD motor off and clean the brushes and the inside magnets with fine steel wool and contact cleaner and lube the bearings with some dry graphite spray and some kind of good oil that wont get too thick in the winter it will wok fine after that and it is pretty easy but when you take the motor off there are like 3 wires that need to be cut and soldered back on don't cut all of them let me know how it goes