We have done the route 81 thing and always use that on the return trip.
Going south from NY state we make it to our in laws near Lancaster pa first by avoiding NJ (very congested). We leave their house and get onto route 95 at 8pm and make it PAST washington DC and spend night in rest air just past DC (the car only one). and then onward we go.
OR leave nj around midnight and head south....