whats wrong?

Everything was fine on and off the expressway. Two days ago while driving around town I noticed the tranny wasn't freewheeling. Instead it seemed to be slowing down like a gear reduction. It would up shift fine. Today I pulled out of the drive way and two miles the truck stalled out while driving. I dropped it into natural started it right up and continued driving. One mile later and it started to high rev but no movement in any gear. I shifted into 4x4 and still nothing. I rolled and stop put in into reverse and it moved a little whit a winning sound then I put it in drive and increased the RPM”S and it crawled forward a block and stopped. I towed it home the tranny fluid level was good and clean with no burnt smell. I changed the fluid and filter year & a half ago.