Quick report on my trip back...
Basically, most everything I experienced on the way up on I-81 was almost exactly the same in terms of the mile marker ranges I posted previously. I-81 through Maryland was again solid/no signal switch once locked on from state line to state line and by far the most consistent. However, I can report that I did hit a new pocket of LTE a little north of Harrisonburg, VA. I just checked the Sensorly map but thus far its not showing up where my perpetual mapping took place, but the range was roughly from I-81 VA MM263-MM256.
Was on a phone call till about halfway down the I-76 turnpike and wasn't able to check the first half, but from halfway from the 283 interchange to the Carlisle exit I got off on I wasn't able to pick up anything other than 3G.