3 speed would like lower rpm's hwy?

Going to a bigger rim will not help. It just changes the size tire on the rim. You can get 26 inch tires for 14 or 15 inch rims. Ride quality should improve with 15's. But not drop in RPM's.

You have 2 options. Bigger tire or overdrive the tranny via auto 4spd, auto w/gear vendors. I don't know if theres a 5 or 6 spd auto that can do the trick, but if the tranny gets bigger, fitment becomes an issue.