Hello, not quite sure what’s going on but would sure appreciate some advise. I recently picked up a daily (2006 s60 2.5t 5AT fwd). It was doing great and continues to shift smooth for its age, but recently whenever I get up to highway speeds (65+), any attempt at acceleration in 5th is just met with a very aggressive jerking and hardly any change in speed and rpm. No check engine lights comes on or flashes though. If I downshift into 4th with the manual selector it jerks a tiny bit but nowhere near as bad. The transmission fluid was pretty dark but I went way over the top and flushed 20 quarts of our valvoline atf through it at work to be safe. It has 179k on it but the motor and trans are 100% dry top to bottom. I don’t know if that’s common for these but I was super surprised to find that. All I’ve done since I got it otherwise is all the spark plugs and coil packs a few weeks prior to this issue. If anyone has an idea it’s greatly appreciated

 

Those volvos transmission need a very specific fluid. Mobil 3309 is one of them, other than that i think its only volvo brand. I would get that corrected sooner rather than later. There are only a few that meet the correct specs.

 

Just had my xc-70 in the shop with this problem, thought it might be fuel pump related. Turned out it was spark plug failure. replaced the plugs, working well on 60km trip home!