Sounds like a multiple injector problem to me. The egr may just be gunked up from being unplugged, and since they most likely tested it connected it showed slow response. I would agree on the injectors though. I'm dealing with the same thing at the moment due to a bad tank of fuel. I plan to have it diagnosed and change the failed injectors myself, possibly the whole bank since I'll already be there. I replaced the right bank a few months ago, so hopefully none of those have failed.