I had the same issue while towing a trailer past Breckenridge. Did your red warning light come on? When you say pegged do you really mean pegged or is the needle just in the red. Are your cooling fans working? Altitude has a lot to do with it.I have a 2002 K1200 to western C0 lt with 18000k on the clock, bike always runs 3/4 on heat gauge ,took trip too western CO. heat gauge pegged on 9-10000 ft passes has water in recovery tank. Any ideas before I have to pull plastic??