I would check the tensioner pully to see if the spring is bad. It sounds like it could be the belt sqealing. Also, check your water pump by trying to wobble the fan. If it is loose it means your bearing is bad in the water pump. I just went through the same thing and the water pump was binding up and making a similar noise. If your plenum is bad you will notice a lack of power, pinging, and you will be losing oil. To check it just take the throttle body off and look down into the intake. If you see oil in there then you most likely have a blown plenum gasket. I just got mine back from a local shop(no dealer). I bought the Hughes Plenum kit, intake gasket and bolt kit, 180*t-stat, a new front O2 sensor, new throttle body gasket, new o-rings for the injectors, oil change, and the water pump bypass hose. That was about $240. I took it all to the shop and they installed it for $350. I could have done it myself, but work simply takes up all of my time. But, I guess for for around $600, at least I know it's fixed now. My problem ended up not being the plenum though. Turns out that when the dealer replaced the plenum the first time, when the truck was under warranty, they didn't put the rear vally gasket in correctly. It was pinched and hanging down, letting oil into the intake. So, I didn't really need a plenum gasket. But, I am glad that I got the Hughes kit and have to worry about it in the future. Hope this helped.