Are there known electrical issues with the 2004 GMC Yukon? Such as intermittent starting issues, seat warmers working sometime, etc.

Please check this website.

ODI - Office of Defects Investigation (http://www-odi.nhtsa.dot.gov/home.cfm)

You can do a search to see if anyone else has complained about this problem or if there is some sort of recall. You can also file a complaint if the dealership is not resolving the problem to your satisfaction.