2002 Volvo S60 Transmission jerking and slipping

I have a 2002 S60 (front wheel drive). A couple of days ago I was idling in line at a drive-thru coffee shop and when I went to pull forward to the window the engine revved, but the car did not go forward. I tried reverse and that didn't work either. It was as if the gears would not engage. I had it towed to my regular Volvo mechanic. My mechanic couldn't find anything in the computer system and recommended I take it to the dealer for a second opinion since it sounded to him like a mechanical problem in the transmission. I was able to drive it home from my mechanic and to the dealer, but it feels like the gears are jerking into place, particularly when starting up from a stop-light. It lurches into 1st/2nd gear. It also very occasionally will feel as though the engine is "surging" for lack of a better word. My foot will be on the break and the RPMs are okay, but it feels like the car wants to take off / lurch forward. That only seems to happen when it's cold outside and the car hasn't completely warmed up. Are these issues related? Solutions to either or both?