Compus and outside temperature not showing on mirror

[A hitch and a hop]

2004 GMC Sierra SLT The indicator on the rear view mirrow has stopped working. I checked with the dealer and was told to check the SIR fuse in the fuse box under the hood. That fuse appeared good, but replaced it anyway. Still did not solve problem. Can anyone offer advise on what else I should check? A concerned that it might be an indication of some other problem. Also, the onstar and other features located on the mirror are working. Only the compus and temperature indicator has failed.