So I recently replaced the transmission fluid and filter. The old fluid looked great still. Was nice red color and there was hardly any metal on the magnet at the bottom on the pan. My problem is when I stick it in reverse when I first turn it on I gotta really push the gas to 2000rpm to get it to move but driving works perfectly normal. After that first initial reverse the reverse will work fine after. I drove it around fir a bit and checked the fluid level while still on and warm and it's good so I am not sure what to do. Before the fluid change it was perfectly fine.

 

Gotta check fluid level in neutral, on a flat surface. Else you get an artificially high reading.

Probably wouldn't have been a bad idea to adjust the bands while you were in there.

Try this though: Start the truck, put it in reverse, wait 20-30 seconds, then drive away. Does it still seem to slip?