If the park service has started already, skip the "slavery was the reason for the War of Northern Aggression". The PC crowd has been jumping up and down to get slavery induced into any battle field tour. Just get a map and audio tape and do the tour yourself, you'll be fine.
Both times I did the tour with the Battlefield guide, all he talked about was the battle. The strategic and tactical situation, the terrain, the movements etc. No BS was included, thank God. It really is nearly impossible to sort out the battle without one of the guides.