Multi-part texts from Verizon to AT&T not being completely received

Friends on AT&T have been telling me that when I send multiple-part texts from my Verizon phone, they do not receive the entire thing.

I am aware that AT&T does not perform SMS concatenation on inbound Verizon (CDMA) texts; the problem is that chunks of the message are disappearing outright. It would be fine if those occasional 400-500 character texts were received as multi-part messages as expected.

I'm on an iPhone 5, currently 6.1.4, was 6.1.3 for past however long it was since 6.1.3 was released. Was jailbroken on 6.1.2 briefly but restored to stock 6.1.2 firmware.

I was told by one person that this has been an issue since I switched from AT&T to Verizon months ago but occurs intermittently.

Have hard reset my phone already.

All I can think to try is an iTunes restore -> set up as new phone. Don't know if calling Verizon would help. Anything else I could try first?

I did give them a call this morning. The last two steps to try before they send me a replacement phone were:

1. Hard reset (already did that)
2. Restore phone as new in iTunes (just did that, testing now)

She said that she has seen all sorts of odd issues be connected to a device as opposed to the network, and beyond that point, they would send a replacement device.

I'd have worried about the network too. Any chance it could be a phone thing as opposed to a network thing? I switched to Verizon specifically because of their coverage and reputation for cell service.

Meanwhile, either the phone or the network is incapable of reliably handling ~3-part texts, and that is not acceptable.

Same thing still happening intermittently. Have had network tickets with Verizon with no real results to come from it. Even with just a lowly 180ish character text -- have had an AT&T recipient not receive anything at all recently.