2001 Silverado 1500 4.8L intermittent stalling

[hammerandnails]

New member her with an extremely frustrating problem - my 2001 Silverado with a 4.8L engine and about 180000 kms on it has an intermittent issue with staying running. Here's what happens:

 

Truck will be running fine and then will either stall or if it has been sitting for a while (i.e at the mall shopping) it will turn over and start but immediately stall. If i keep the engine idlled up it will allow me to shift into gear and drive. The other issue it will have is it will turn over and start but will not stay idling. I have taken it to a mechanic who put it on a diagnostic machine and it didnt show anything wrong and it doesnt have this issue all the time. He cleaned out the EGR valve and it seemed to go away for a while and he figured that might be the issue but suggested not to replace it as the diagnostics showed everything was fine and it may be a waste of money.

 

My question is do I bite the bullet and replace the valve or could it be another issue? The truck will run great when its cold out (never have the issue in the winter) but if its hot out or its been driven for awhile thats usually when the problem shows up. Again like I said before though its an intermittent issue - it can run weeks in the heat with no issues and then other times it does this on the first start of the day.

 

Any suggestions or help are appreciated and thanks in advance.