Colo Spgs FD Truck 51?
It could have also been a Cheyenne Mountain Air Force Station truck. I heard them say on their Air Force trunked radio system that they were headed to a medical call in the city during that time.
FDs from the 4 Air Force bases ran calls for accidents, medical, and other calls in the city during the recent Waldo Canyon and Black Forest fires.
I was going to listen to the archives to see if I could hear what you heard about Truck 51 but it seems like the feed was locked into CSFD-4 so didn't hear the dispatch channel. My scanner was also locked onto 4 at that time.
Pro-106 (saving to Pro96Com), 396XT (saving audio and metadata w/ProScan), and SDR dongles