Hello guys, new member here. I bought a forester 2012 x limited at 138000m. I noticed it lose power after running for a while and it get very slow. For getting the power i have to press gas more than 70% and it shifts the gear to 3rd and get the boost. I found the transmission oil is not in a good shape and its brown. I have changed the spark plugs, cleaned the throttle and cleaned the egr. I also reset the throttle. The car is more responsive but it slown down after running for a while.No check engine or engine codes. Can anyone suggest me something why? Also should i change the transmission fluid as i dont know it had been changed before or not?