05 Sport pops/slips out of gear?!?

So it tends to happen between 3rd and 4th gears, approx. 30 - 45mph. I'll be driving along and all of the sudden, it makes a pop sound and I'm in neutral. Drive line disengaged. I have to put the clutch in and shift BACK it to whatever gear I need. Any suggestions?

(86K miles and a 3" lift w/o diff drop in case that matters...)

 

Not good, I would start by checking your transmission fluid, making sure it is full. Have you changed the fluid before? Is it doing anything else odd, any grinding?

Im not sure on the service timeline for the manual tranny fluid, but i believe a lot of people suggest some nice synthetic oil, like the redline 75-90 GL-5 based stuff(please someone correct me if im wrong, this is what i remember it being called) . I used this in my old Toyota pickup and it actually helped smooth out my shifting. By the way is it a 5 or 6 speed just for more info to anyone else who replies.

edit: actually i think it was the Non-NS version

 

6 speed. Transmission fluid all good. Hummmm