I've noticed while idling today and yesterday an intermittent hiccup/stumble idle fluctuation. Happens when engine is at operating temp and with or without my high idle switch on, in park or in gear. This is very intermittent so far, and no check engine light. Truck runs and starts normal. Took out on highway=runs good/full smooth power and boost levels, no smoke at all when this happens idling. I am thinking its possible my EGR valve is starting to act up, but I'm not sure. Tonight it ran fine without any hiccup/stumble at idle. 52k on the truck so far. Any input is welcome.