If you have the brown silt in the system, flush and change the coolant
now. These trucks are prone to intake gasket failures. My friend at GMC and
I, believe it is due to the Dex-Cool coolant, but there is no documented
proof of this as of yet.
Watch for intake gasket coolant leaks. Check your oil for coolant
contamination, when you change your oil. Also check for external leaks. If
you have had to add coolant regularly, you may have an intake leak. Check
your radiator cap too. My factory cap started leaking at 40K miles. I
installed one made by Stant. It's been doing great so far (1 yr).
External intake coolant leaks, are more common than internal, on this
P.S. I worked for Pontiac/GMC for 8 yrs. I now work for a municipality, but
retain my contacts at GM in good faith (The machanics I worked with). They
give me all the inside information.