While I fully understand that TV boxes are big, this is a good argument for keeping them, as well as the rest of your boxes.
U-Haul's TV boxes go up to 70", but you may check with the local Best Buy or some other TV store to see if they can keep one for you. Are you staying in the same city? If so, find some large sheets of cardboard, buy some moving blankets from Harbor Freight, wrap it and lay it face down in the bed of your truck with plenty of packing under it and drive very carefully. Drive when there's minimal traffic. If the pickup is a crew cab and the floor is flat in the rear, maybe you could stand it up and lean it against the back seats, with the seat belt keeping it from flopping forward during stops.
You could also rent a van and strap it to the side, using plenty of padding. If it's a short trip, U-Haul and some big home building supply stores rent them at a fairly low cost. If you hire a good moving company, they'll know how to handle it.