You took too long time! I finished Shiloh as CSA yesterday on brig. gen difficulty. I would say that: Don't have long and prolonged firefights against Union. You need to be on advantage all the time.
First phase is church; Here I sent skirmishers and one inf brigade to right side of map, fighting with the union skirms and troops just to keep them occupied. Always having my men in the woods to make sure they will last. During the time I marched with rest of my army undetected on left side preserving the stamina of my men. When at the river woods near the church far left, I order my men to run, all at the same time, over the river to quickly assault and capture the church. I do it even before Grant appears with reinforcements, thus ending battle prematurely!
Second phase; the same tactic here with sending skirms to right to pull enemies and keep them occupied, left army preserves stamina until cap point is near and then all sudden charge. Ending battle prematurely.
Third phase, the hornets nest. By doing circumventing tactics the union troops are trapped south of my CSA troops at church and second phsae. I leave skirms behind me to keep them occupied while main army surround hornet nest and make devastating firing into the nest. I keep my cannons very close and soon the unions will break and a few shatter. Then I capture the hornet nest prematurely at the same time as I move all my main army to the end of map north of hornet nest.
Fourth and last phase, Pittsburgh landing. There's only artillery and ironclads protecting the landing, and my main troops quickly reach it as they are close being north of hornets nest. I dont give the enemy artillery a fuq and quickly swarms the fort routing the artillery. Then I place my troops as a wedge with point facing north in pittsburg landing, all in the woods. Awaiting Union reinforcement from north. Defend hard and use your generals to boost your men's morale and have artillery batteries very close to fire canisters and shells all the time.
I managed it with only 30% casualties.
My Army setup pre-Shiloh: 1 Corp, 3 Divisions with 4 brigades each.
9 Infantry (you need backbone for strong and coeherent assalts and be able to depatch 4-5 skirmishers)
1 Artillery
1 Skirmisher with high grade snipers
1 Mounted infantry
How would I have done it better?
I would have exchanged the skirmisher brigade with expensive rifles to another Mounted Infantry brigade as they excelled and was invaluable in the Shiloh grand battle.