This problem is related to the low coolent light coming on when engine starts but the water level is at correct level.

G.M service bulletin # 990602016

That bulletin was for a reposition of the coolant tank due to angles being incorrect, and having to shim the front mounting stud, to bring the level correct in relation to the sending unit at the rear of the tank.
The washers go between the surge tank and the
fender well, on the stud, to raise the front of the tank