I have a 2005 Ranger Fx4 that i bought 2 weeks ago, the first time i try the 4x4 in a muddy field i found out it wont stay engaged. Its has the electronic switch and automatic locking hubs and the light goes on on the dash that says 4x4 and it doesnt turn off even when i get into higher RPM the 4x4 gives out and somthing grinds a bit, but the 4x4 light stays on. if i keep it slow and dont rev to high it stays in. and when it does fall out i let off the gas and it kicks in again at lower RPM. I really dont want to take it to a mechanic if i dont have to!!! any suggestions?