I live in NYC and recently noticed 2 day prime deliveries are becoming more unreliable. I've had two shipments in the last 2 months take 3 days. It seems they're switching to using USPS in place of UPS for many shipments, and those are the ones I'm seeing problems with.

These USPS shipments often show tracking information that refer to handing the package off to a "shipping partner". They don't say who they're using, and then things go dark on the tracking information until it gets to a post office.