Sorry to say I have never been to Gettysurg...want to go there someday as its reportedly the most haunted location in North America!
I've been to Shiloh (in West Tennessee) a few times since my dad lives pretty close to the battlefield. It was before my ghost hunting interest really got going and also during some of the hottest days of July and August.
I clearly remeber some chilly spots, even though it was badddd hot! Over by Bloddy Pond and the Peach Orchard were two places that seemed active. I kept thinking I heard people talking when I was alone and no-one could be seen anywhere.
Bloody Pond is not very large at all but its quite shaded, due to many trees growing around it and thick woods behind it. Its creepy, even in the middle of the day.
I'm going to Shiloh again on July 4th weekend...will be staying until the Park closes (10pm) and snapping some pictures at various locations...
Would love to take some short MPEG movies if I can get my camera settings right.
There are mass Confederate graves where I plan on placing a digital recorder on one in particular. The Union troops were buried in a nice cemetery since they won the battle, but they literally pitched all the dead (and a few still living I imagine) Confederates in 5 seperate large graves in different locations.
Good luck if you go to Gettysburg...you'll probably find lots of interesting locations and people from the present (and the past).
PS: I've seen TV shows that metnion "Devil's Den" as being a really hot location as well as Little Round Top.