whats up with this?

[tphsmith]

today I drove about 100 miles in my truck and 2.2 miles from home I turned the street corner and gave it gas to proceed and all the truck did was wind up the motor, I thought umm, maybe it slipped out of gear. No it did not slip out of gear. I put it down in low drive and it took me about a block farther. I got out of the truck and checked the tranny fluid, the fluid was a tiny bit below full mark, maybe a quart. a friend of mine drove me to the house to get 2 quarts of tranny fluid. I poured 1 quart in the tranny and it showed full. the truck starts and you can run the automatic shiffter threw the drive line locations and the linkage travels with each shift. the tranny filter had been changed about maybe 600 miles ago and the fluid looks good. i cant smell any burnt oil smell and it dont run out of the tranny. the truck does not roll by pushing it when its in park but all the other gears you can push it all over the place.
what the heck is going on with this tranny?. when I put it in drive andgive it gas the drive shaft does not turn, so I'm sure its something with the tranny.
please help. this is my daily drive and only transpertation I have. and I got to get it back on the road. WHAT DO I DO?