I've got a 95 Ram 1500 with 360/46RH.....It got dunked in a swamp and would not shift once we got it out. I dropped the trans pan and it was full of dirty pond water and trans. fluid. I changed the fluid and filter several times and the fluid in now clean. I took the truck for a ride and it will not shift out of first gear. Any thoughts on what could be causing this. It pulls hard in first (does not slip or hesitiate). Just will not shift up...