My dad has been complaining about this exact same thing, while I'm staying with him during the holidays I've ordered some stuff to his house as well.

Every single thing he's ordered has been 1-2 days late, every single thing I've ordered has been on time w/ 1 and 2 day shipping. All shipped to the same address, both of us on separate amazon prime accounts. (sample size ~5-10)

Does amazon keep an internal tier-list of customers and prioritize based on this?