Idles issues

I have an 05 Duramax 2500 with a 6 spd manual trans. I'm having an idle problem, think it may be a bad injector, but I want to hear what you have to say. It will only do it once the truck is warm, but not all the time. When you come up to a stop sign and the clutch pushed in, it acts like it has a miss. The gear shifter will start shaking from side to side, the whole truck feels like your driving over a rumble strip along the highway. But it will stop if I increase the idle RPMs up to 900-1000 rpms. It will do the same thing, if I jump out of the truck to open a gate, it will start to make a noise that resembles injector clatter, but as soon as I give it a little rpm it will quit. Whats aggrivating is, I took it to the dealer to have them check it twice and I can't get it to do it while I'm there. There isn't a way to check the injectors unless I let the dealer do it or I pull them out to be sent off and tested. Any input you guys have would be appreciated. It has 149,xxx miles, fuel filter change 5k miles ago, air filter replacement 5k miles ago, and its bone stock.