My d1 with 150k miles all of a sudden started only working in 1st and 2nd gear. I dropped the pan last night to change the fluid out and probably around 6 quarts drained out. I added fresh fluid and it still won't shift into the higher gears. Should I take it to a shop to have the fluid completely flushed out? Trying to get this fixed so I can go see my family for Thanksgiving.