Hope this helps....
Well everyone else has some pretty good ideas, however the problem you say only starts when you put it in drive?
Well if you have an auto, then check the detent cable, because if the engine drops and stumbles, then there is no way it will hold much vacuum. That cable is the only thing I can think of that would make the engine poop out in drive...
Also the only other thing I would do would be to check the fuel pump pressure. Besides that I have no idea.
Also you said there is gas in the egr valve block off, sometimes manual pump gas diaphrams break and leak gas into the engine, which thins the oil, check your oil also because if your oil thins it is pretty easy to get my your oil rings.