Hey y'all, first time posting here, long time lurker.

I've got a 2006 Sonata with the 3.3 V6 and auto. I picked it up for $700 when my truck began to have major issues and I was in college. I absolutely love this car, but lately I've been having some transmission issues. Car has 139k miles on it.

It's pretty random but becoming more frequent, shifting into reverse will result in it slamming into gear, like it's applying line pressure. Then shifting into Drive range, display indicates drive, but no engagement, as if it was in neutral. Shifting manually, the display shows D1/D2 as expected, but no change. No codes stored, no check engine light. Sometimes, I can just let it sit in Drive for 15-20 seconds and it'll eventually engage, or shutting it off and restarting it sometimes does the trick, although that may be coincidental. Trans fluid is at the correct level. I have no idea when it was last serviced. The only history I have on this car is that the previous owner had the range switch replaced approx 21,000 miles ago and mentioned there was other trans work done, but I don't have the invoices for any additional work.

Any ideas? I know that they are prone to liquid getting down the shifter area, but I know that hasn't happened since I had the car, and it hasn't been driven through deep water or beat on hard since I've had it.