I bought my automatic 2006 Mazda 3 2.3L about 7 months ago with only 82k on it. It's in good condition, have had to replace the transaxle and that was the biggest repair so far. Previous owner bought it new in 2005 and was a careful driver with it. Now, 7 months and 8k miles in, it randomly switches gears. I'll be going 45 mph and it will switch from 5th gear to 4th and then 3rd. Sometimes it refuses to go up to 5th gear altogether. I put it in manual and it switches gears perfectly fine. And this all happened today. Hadn't had a problem like this before.
However, ever since I bought it, when the car is coasting, the rpm will rev down past 1000 and stay there until I push the gas pedal. Not sure if that's related or not. Is my transmission shot? Any advice?