Sometimes when my 2.5L 2000 automatic Liberty (Legacy) changes up gears I get a loud thud and the vehicle is shunted forward. This started happening on odd occasions a couple of months ago and now happens most times i drive but only after the car has been running for a while (20 or 30mins).
Once the thud/shunting starts occurring it happens for the rest of the trip whenever the gears change up.
Every time this starts happening I also have loss of power at low revs (ie taking off from traffic lights).
I have checked the error codes and TPS codes shows up (No. 31). I have replaced the TPS but still have the problem.