I just put new 20's on my 04 Denali and I'm getting a "tire service message" appearing on my display. Can I clear the message or does the dealer have to clear it?

thanks

You will have to get the truck reprogrammed for the new tire / rim size.

Did you use the old valve stems from the rims that the truck came with? (I'm assuming that this has the tire pressure monitor system) If not you may be SOL without replacing the passenger door module to one that is made for a truck without the tire pressure mon. system.
(The Pass. Door Module receives messages from each of the wheels tire pressure senders.)

GM may have come up with updated software to "switch" to a non-monitored system, but I haven't seen it yet.

Hope this helps.