I can only give you my recent experience. I had much different but bad transmission problems, and their was nothing that I looked into that I could have done myself. The dealer will charge you $5,000 and up for a new transmission and labor. My suggestion is to go to a reputable independent transmission shop and get the codes read. If there are codes, then there may be solenoid or other electronic problems that can be fixed. No codes just means the mechanicals are failing. The shop will probably ding you $2,000+ for a rebuild with a year warranty, no matter what the problem actually is.

One thing to try first is a transmission flush, described in detail in many past threads (or get the kit from ipd for fittings and instructions). Use Mobil 1 synthetic transmission fluid and see if it helps. You're betting $100 on a low probability fix, but then everything else is going to cost you dearly.