I had to recently drive through PA, did a trip from Virginia -> Allentown -> Honsdale -> NY

The back road speed limit signs were all over 25, 35 45... In weird places. The thing that gets me though is almost ALL of the locals just speed like crazy! I'm following the speed limit on the high way cruising along at 55. Getting passed by hicks going way way over the speed limit. Flying past me. (And tailgating... Think that is happening all over now-days...)

Is this common in PA, just fuck speed limits?

It's pretty variable by where specifically in PA you're at, but in my experience... yeah, unfortunately

I'm in deep redneck Pennsyltucky, and speed limits out here are more like suggestions. You'll pretty much never see any State troopers on the highway, so it's pretty common to see people going 80-90 in a 65 zone.