Shifting problems

I had about 6 inches of water inside my truck during the hurricane and when the water subsided I checked all the fluids and it did not appear that any water infiltrated the rear end, or transmission. I drove the truck about 100 miles and then it started to be slow to shift for about 3 miles then on the way back to my house it would not shift. I would let off the gas to lower the RPM and when I went back on the gas it would rev but no power to the wheels. I pulled over and checked the fluid and it was good. I started again and got up to about 35 MPH and it was not shifting and I let off the gas and when I gave it gas again it would rev but not power to the wheels. I parked the truck and came back about 4 or 5 hours later and was going to nurse the truck home and it pulled out and shifted and got up to 50 MPH and was fine for about 10 miles then it started to no shift again. What could be the problem? 279K miles