The quick-connect fittings for the heater hoses tend to leak engine coolant. This problem commonly occurs because the metal housing has become brittle, which can break and cause leaks.Google+
Car Problem Reports
Chevrolet Tahoe Quick-Connect Fittings For Heater Hoses May Leak Engine Coolant
Chevrolet Tahoe Problem
Average Mileage: 129,657 mi (45,971 mi - 173,000 mi)
Visitor, 1999 Chevrolet Tahoe, 45,971 mi
this appears to be my identical issue.
leaky quick connects may leak fluid