What is the gross weight of a 24ft truck?

Depends on what model truck it is. Generally speaking, you can expect the manufacturer to rate them at 26,000 lbs, in order to allow them to be sold as non-commercial vehicles. However, many of them (such as the Ford F750) come with 31,000 lb axles. The max allowable weight on a single axle truck is going to be 33,000 lbs., but anything over 26,000 requires a CDL.