I am having the same problem, maybe i made a mistake during the course of the campaign but i won all battles and lost none. Draw Shiloh and Mallvern Hill.
I get my ass kicked first try with 2nd Battle of Bull Run. I lost my cavalry and a whole lot of infantry during the first phase where you have to lure the enemy. I will try to use your tips, but something tells me my force wont be able to do the job got no cash, only a few battalions have good rifles. See attachments for my army.