I found a old thread '06 with the same unit and symptoms. Their problem turned out to be excessive wear on the cam lobes. I tried to gage the lift of the valves and the exhaust seemed very small,the intake seemed ok. I opened the cover and pulled the camshaft and the exhaust cam lobe was only about a third as high as it should be, ground right down. The fuel pump lobe also showed wear but the intake looked like new? The exhaust lifter didn't't show wear either. I bought a new one and will try to get it all back together next week and see what happens.