GM-GMC: Fuel valve, second tank, fuel valve

Question
I have a `79 3/4 ton full time 4x4, with a re-built 350, and auto trans.. I just bought it for a farm truck. And have been thru 2 tank switching valves(the org. 1 and a used 1 from the junk yard)I ordered 1 from the chevy, and they said that this is a hard part to get. Am I to expect these problems with this fuel system?

Answer
My recommendation to you would be to drive it until it happens again, and it will, then remove the fuel valve and only use one tank.  If it is a farm truck and you are not travelling great distances, you won't need the second tank.  I have seen ALOT of those valves malfunction, most people need both tanks, but if it is a farm truck, that would be my recommendation.  Problem gone.
Hope this helps