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.
Car Problem Reports
GMC 1500 Pickup Quick-Connect Fittings For Heater Hoses May Leak Engine Coolant
GMC 1500 Pickup Problem
Average Mileage: 144,000 mi (135,000 mi - 153,000 mi)