Wilmington NY to White River Jt Vermont

Trip Planner makes some odd choices at times. Why does it send you on a route that you cannot actually negotiate? In your case, it is just silly to give you a route with what looks to me like it has two low clearances. The Good Sam answer, "you can drag the route to avoid." Well, if you are not familiar with an area, where the heck do you drag it? (Trip Planner tried to send me on two parkways in CT and NY that do not allow motorhomes). Having lived in central Vermont for 40+ years, I don't like the route from the bridge to White River. The Green Mountains are not the highest in the east, but I would not choose to take either of their suggested routes over them. Route 4 in Rutland would be my choice. Your best bet might well be the northern route with the ferry if you find your rig is under 13' 6". Those ferries carry tractor trailers all the time and most of them probably push the 13' 6".
Anyway, you are traveling through some great country - enjoy - travel safe.