Pennsylvania stacks UM/UIM limits across vehicles unless you signed a waiver, and its limited tort option can cost you pain and suffering
Pennsylvania's rules are in 75 Pa.C.S. 1731 (offer and rejection), 1738 (stacking and the waiver) and 1705 (limited and full tort). Definitions are in 1702, fault in 42 Pa.C.S. 7102 and the deadline in 5524.
Read how stacked and single-limit coverage differ in Pennsylvania, check what section 1738 says, or see how Pennsylvania UM and UIM work.