Almost everything I can get delivered free in 3 days, if I pay $6 I can get it delivered in 2 days. 
The last 2 orders (free Prime trial) they DID DO , FREE 2 day shipping, but 1 order shipped 3 days AFTER I ordered ( free 5-day delivery) the other shipped 2 days after the order (free 4-day delivery).  I looked at both before ordering both would have arrived in 2 days if I paid the $6 shipping.