Hot or Cold, My TA takes off just fine in 1st, shifts hard into 2nd, but as soon as 3rd gear hits, its like I shifted into neutral. I can't event get it to attempt 4th either. What happened? The fluid is full, and doesn't smell burn't either.

 

3-4 clutch pack is gone need rebuild.

 

just like that it can go out?

 

Same thing happened to me a few years ago with my 700R4. I was driving normally and it went to shift to third and, like you said, it felt like it was in neutral. It never went to fourth gear either like yours. I never did open up the transmission to see what happened (it's still sitting under my porch at home) but people told me the same thing about the 2-3 clutch pack. I decided that instead of rebuilding it, I would swap in a T56. I've never regretted that decision.