1) Make sure that the scanner firmware has been updated so that it will work with rebanded 800 Mhz trunked systems.
2) Make sure you program the frequencies for trunking, not conventional use.
3) Make sure you enter the CSP Talk Groups.
If you don't know what a trunk system is or how to program the 796 for trunking, you should do some research on the RR Wiki. You can start here
Uniden has information on performing the 796D firmware update here
Here is specific frequency and talk group information for the CSP