I bought my Mopar warranty through a different dealership (Robbins Motors) about three months after I purchased the 19 Laramie. My understanding is the cost increases after 12 mo/12,000 miles if you wait. The longest Mopar warranty is 8 yrs 125,000 miles with $0/100/200 deductible options. Remember that the 8 yrs and mileage coverage starts on the day you buy the truck so it's really a 5 year extension. Cost should be around $2400 for the 8/125 $200 deductible.
What you gain by buying before the 12/12 time frame is lower cost for the policy, key replacement, guaranteed rental car coverage, although limited, and some other things.
My dealer didn't even want to talk about the Mopar coverage as he was pushing a third party one for over $4500 so I just declined and bought the Mopar one at the cheapest seller I could find.
I had a third party warranty on my 14 Ram from Fidelity because it was a Canadian return (no Mopar Warranty available). While I was reasonably confident they would pay for repairs, after talking to them, it seemed they would cover with no discussion repairs at a facility they had agreements with and none in this area were Ram dealers. They said they would cover at other repair shops but I seem to recall that it took discussions with the shop and Fidelity. Seemed like a bit of an issue if I was traveling outside my local area. I like the fact that the Mopar plan covers it at all FCA dealers just like the 36/36 initial warranty with a few minor differences.