I have a 2000 ford explorer 4.0 SOHC V6 4x4 automatic transmission with 84,000 miles in it. It has a problem in the drivetrain, when i put it in drive it will not go, it just revs up, but when i shift to reverse it works just fine. If i put it in low gear 1 it tries to move but it still does not go. I keep hearing this clicking noise coming from underneath the truck somewhere in the transmission or the transfer case. I checked my transfer case fluid and transmission fluid and it is good. Can anyone let me know what could be wrong with it?