I would concur with Yukon on timing. The guide is a fabulous tool for planning and accurate. Be sure to help the GMC by buying one. If you are not going for speed, plan in the vista trails to break up the green tunnel. Not an option in May, a lot of them, as already mentioned. Just a couple of favorites...Glastonbury Fire Tower,Deer's Leap, Killington Peak and Camel's Hump. Awww, just do them all! Years ago I did a Souther during foliage and it was fantastic. I was fortunate to beat the snow on the trip; it can be iffy that time of year if we are snow lucky for making time. You would want to start in the north for the fall and follow the foliage south. Need heavier gear, I had some five degree nights on that trip. Reverse you would find the colors past by the time you get mid trail. Have fun..wax on....water proof boots in May unless you like wet feet for several hundred miles.
If it moves, you can eat it.