* Class A - Any combination of vehicles with a GVWR of 26,001 or more pounds (11,793 kg) provided the GVWR of the vehicle(s) being towed is in excess of 10,000 pounds (4536 kg).
* Class B - Any single vehicle with a GVWR of 26,001 or more pounds (11,793 kg), or any such vehicle towing a vehicle not in excess of 10,000 pounds (4536 kg) GVWR.
So if you are towing a big chipper, you are more then likely over the 5 ton weight requirement.
Air breakes on a CDL is not an endorsement, but a restriction.
L Restriction - Prohibits driving of vehicles with air brakes. The CDL will carry this restriction unless you pass an air brakes knowledge test and a skills test in a vehicle equipped with air brakes.
Now, if you are not going to tow anything, and want to put off the CDL for a while, you could get a tare weight from a certified scale company. Then put the that on the side of the truck and keep the certificate from the weighing in the cab with the required paperwork.
Tare weight is when a container is completely empty, so you get every possible removable pound out of the truck you can before going on the scale.