I have a 2008 S40 (87K miles). I recently had the transmission replaced due to an unfortunate encounter with some concrete and rebar on the road. The very next day after I got it back from my mechanic, I feel a shudder and I get a warning light (red triangle with the exclamation point) and a message on my dash saying "SHIFT UP OR SLOW DOWN". I managed to drive through it, and figured it was a glitch/something to do with the new transmission. Not so, I have noticed that it started to shudder whenever I hovered around 40-45mph. It would shudder, seem to find its gear, and accelerate as normal. Took me awhile to get it into my mechanic, and the code that came up was multiple misfires.We decided to change out all 5 coils and spark plugs. Thought that did the trick, nope, on the drive home from the mechanic, it shudders again and I turn around and go straight back; same issue, same code comes up. I left it with him for 3 days to figure out what is causing the misfires. He cannot find it! Told me today that he cleared out the computer, reset the parameters and said he was driving it fine. As soon as i go to pick it up, on my way off the property, shudder, engine light comes on, and we're back at square one! What could be the cause!? My mechanic, (who solely works on Volvos and has a very good reputation and business amongst many Volvo owners) is at a loss. Any ideas? Anyone?