Truck drove fine and have had no problems with the transmition. Parked it went into my appointment came out and started it. Put the truck in reverse and backed out. It acted like it didn't have the power to back out. The 4lo lite is on and the transmition won't shift when driven. Help please.

Low on fluid, clogged filter, modulator valve(if so equipped), speed shift sensor. Best to take it to a couple of shops for troubleshooting.