I have been having the same issues, I order in the mornings, all before 10AM central time, i have placed 6 orders with about 40 items in 2 months, and 2 items (of a 4 item order) came in 2 days (i don't count the day i ordered as a day, so the 2 items came in 3 days, which i can understand), I have an order for a 5 Quarts of OIL (wanted to order 4 but they had 2 in stock, ordered and said only one was left) sitting at "waiting to ship" since Nov 25th (fulfilled by AMAZON, so not a 3rd party) yesterday they showed it in stock so i Ordered 3 more. Today the one from the 25th shipped, and 2 from my order of 3 shipped today, the 3rd is in "waiting to ship" and it still shows in stock. I ordered Oil filters Dec 1st, and it arrived today, the 8th. A door hanger clip was ordered Nov 28th (with 4 other items) 3 arrived on the 6th, the door hanger arrived today.
I get the NON amazon sellers may not ship as quick but the actual AMAZON items should. I have had Prime for 4 or 5 years, up till this last year I would say 95% was 2-3 day, again I make sure I order in mornings and consider 3 days including the day i ordered correct, I don't count Sundays ever. But this last 6-8 months i would say 10% has came in 3 days.
its not to huge a deal, non have been deal breakers, but its happening all the time. My subscription to PRIME is for the shipping, I dont use the TV or Music parts of it, and when i purchased it 4-5 years ago that was its selling point, shipping time, all this other stuff has raised its price and I have kept it as I like my stuff quickly. I wont be canceling but I would like to see an improvement.