I was thinking more that the fuel is weak as it is always the bottom 2 cylinders, and when I take the plugs out they are filled with fresh unburned fuel after I shut the engine off...it seems they are drowning out the glow plug. Also as mentioned, once in a while after a few minutes of steady idle, when I punch it to full throttle...ALL cylinders fire properly and the engine sounds fine, if only for a few seconds before the bottom 2 cylinders kick out again. This seems to suggest the timing and intake valves are fine...the fuel is not igniting as it should at the bottom 2.