I recently replaced the engine in my 1998 Z71 parts getter. The issue is when the engine cools down both radiator hoses close down. I took the cap off and the radiator sucked air. The replacement engine was a new crated GM 5.7 four bolt FI vortec 2002 intended for a 3/4 to 1 ton van. It was complete with all sensors, water pump, FI, pan, and torque plate. It was a plug and play installation. A good thing I have not installed an engine in 40 years. It felt good. Does anyone have any ideas?