1999 tacoma possible problem with rear end

[chiggins]

I got into my truck one day after not driving it for 2 or 3 days and reversed it out of its parking place fine. Once I put it into drive, it would not go anywhere and started to spin tires. So it will go into reverse fine but not go forward. I had it towed to a local shop where they put a camara in the rearend and looked to for damage but could not find any. They took the fluid out and there was no steel shavings present too (a major sign up problems). Once they pulled it out of the shop, it stopped doing the problem. they could not find anything wrong with it. Now a week later, I am having the same problem but it will move after I rev it up, it seems like its breaking out of being stuck.
What I want to ask is if anyone else has had this problem and what exactly was the problem/solution. I have a baby coming this month with my girl and need to actually sell the truck to get another 4 door tacoma.

Thanks for everyone's help in advance...

-Chris-
1999 Ext cab Toyota Tacoma
3 inch lift RoughCountry
33inch BFG ATs