I have a stock 2005 Chevrolet 2500hd WT with the duramax. When driving for 15 or 20 miles at a constant speed of around 65, I'll notice black smoke coming from the exhaust going up small hills. I also notice a complete lack of power and I can't hear the turbo spin up, just lots of black smoke. I changed the air filter and cleaned the maf sensor but this still happens without the truck throwing a code and this problem is only intermittent, but now I'm noticing an increased amount of black smoke just starting off from a stand still. I've evan noticed other dmax's out accelerating me with little to no smoke while my truck can't seem to belch enough fo the black stuff. I took it to 2 different dealerships and they just tell me everything is normal. Any ideas would be greatly appreciated and thanks in advance!