I'm no PA resident, but is this it? Open Subchapter A - General Provisions
175.4 A registered vehicle moved upon a highway shall bear a valid certificate of inspection except for ... (you are not under 3000 lbs., so no exception)
you don't fit into the semi-annual inspection; so,
175.6. ANNUAL INSPECTION.
Other vehicles, including emergency vehicles
and private noncommercial vehicles used to
transport students, shall be inspected annually.