From what I have read on the Silverleaf website, the information it displays comes from the Diagnostic connector (same as Aladdin) so whatever data the engine ECM reads has can be displayed on the Silverleaf. Information coming from the engine ECM includes RPM, temperature, oil pressure, boost, cruise on/off, etc.
But Fuel Level is not something the engine ECM has information on - so there would need to be a separate connection or "device" for fuel tank level sender to send that information to the Silverleaf. I did not see such a device listed on the Silverleaf site.
Do you know if you have something like that ( I would expect that device would be located under the dash and would be connected to the original/factory wires that attached to the original fuel gauge.