My Chevrolet Captiva doesn’t shift from 3rd to 4th gear in cold weather; it shifts after a few minutes (2–3 min) of driving. (By “doesn’t shift,” I mean the car doesn’t lose power, it just stays in 3rd gear as if it’s the last gear.) It also shifts roughly in 1st and 2nd gear, but only when cold. The problem completely disappears once the engine warms up. I bought the car at 137,000 miles and I don’t know if the transmission fluid was ever changed before. It’s currently at 165,000 miles and I haven’t changed it either. What could be the cause?