Pennsylvania only had one regiment represented at Shiloh, in fact this is the only Eastern regiment at Shiloh. It was part of Buell's army and arrived on the field on the morning of April 7th. Its supreme moment at Shiloh came near the end of the battle when it captured two cannon plus received the surrender of Colonel Battle of the 20th Tennessee. Both of these moments are detailed on the monument.
When they erected their monument they published a book, as most state organizations did, detailing their efforts in the battle and in getting the monument. This book does double duty as a regimental history, a copy of the book can be found here. This book is also interesting because it includes a copy of David W. Reed's history of Shiloh. Reed was the first historian at Shiloh, he was the man responsible for the cast iron plaques one sees today when they visit the park. He also wrote a history of the battle which is difficult to obtain. The University of Tennessee Press will be coming out with reprint of Reed's work, with the help of Tim Smith (I'm not sure what editorial changes/additions Smith is providing). In the meantime you can see Reed's work for yourself in the 77th Pennsylvania's regimental history.