I've been rereading Bruce Catton's "Never Call Retreat". He has some interesting perspectives on some of the things going on along the Mississippi. For one thing he states that Grant was actually junior in grade to McClernand and that he and Grant were wanting to use the same men for the "glory" of capturing Vicksburg. Catton seems to contined had McClernand and Grant actually joined up the McClernand would have been in overall command. That Sherman was actually ordered to turn over his command to McClernand.

Part of the problem was the Washington politics which pitted McClernand and Grant against each other to get both to move. I can see how this would cause difficult feelings between the two and not fostered a spirit of cooperation.