The first thing to check if your Gravely riding tractor does not bag the grass is to see if the engine is running at full throttle. If it is not running at full throttle, then it might not bag the grass correctly or at all.
Next, check the chute to see if it is clogged with grass and other debris. Clean it out after every use.
Also, clean the blade(s), remove any grass and other buildup. Check to see if the blade is on tightly and that it is not bent. If the blade is bent then it would need to be replaced.
You can find the model and serial numbers on a tag on the main frame of later model Gravely riding tractors.
The model number for your Gravely tractor will be 6 digits long and start with a "9".
NOTE: if you need a part for the small engine in your Gravely lawn tractor, there will be a separate model/serial number for the engine. Here are the small engines that are available in your Gravely tractor. Visit the page of the engine you have to find out where the model/serial number is located for your small engine model: