please let me know if you get this figured out. my 01 ssei does exactly the same thing. I drove mine last night on the interstate and it bothered me so bad, I started driving the car in 3rd gear instead of overdrive to eliminate the "searching"
i bought mine to the tranny shop and they scanned it and they said its not actually the trans. its a miss in my engine. they said lots of people even mechanics bring in there vehicles for that and is a miss,