backfires, blows fitting out of valve cover
 

My work truck is a 99 silverado with the 4.3 six Banger.first start each morn is fine starts so fast you can't get off the key. Later in the day it has to crank for 10-15 seconds or longer.that is I quit cranking then try again. Finally will start. However about 1 in 30-40 starts it will backfire. When it does smoke comes out from under the hood andthe fitting on the end of the hose connected to the PCV valve blows out. I open the hood and it snaps into place, I start it and may run rough for a half minute or so. Then the process repeats. I took it to the local dealer and they put it on the machine.fixed something, charged me 300 bucks and sent me on my way. I lack confidence in them. Any ideas?