1995 Ford Explorer Transmission trouble

2 Days ago I was driving my 95 Ford Explorer and while driving the motor started to rev higher but the car’s speed didn’t increase. Yesterday I was going to drive it, but it didn’t do forward or reverse. I tried shifting thru all the gears, but none of them made it move. The “check engine light is off". When I moved the shifted it to Park with the engine running it makes a grinding noise in the gears before engaging into Park, so this proves that the transmission is working. I looked underneath the car, and another guy was moving the shifter thru all the gears with the engine running. When he shifted it to Park the noise seemed to be coming from the rear of the transmission and the driveline’s front. Another thing is that with the engine off, the transmission in Park, and the rear wheels off the ground I am able to turn the driveline frontward and backward. I think that the driveline shouldn’t move when the vehicle is in Park. ( The 4wd not working since me bought 2 years ago this not matter ), May You help me? Thanks : Franky