Can a 2018 smart prox key be programmed to a 2015 lariat that uses a smart key?
I like the newer key style and the ease of accessing the hard key to occasionally lock the glove box etc.

 

I figured this out today... Yes it works. I have a 2018 key sync'd with my 2015 Lariat. All functions including proximity work.

 

Can one program themselves or is it a trip to the dealer?

 

I ordered a key from Amazon and then found a youtube of how to program/sync the key. This video should get you going: The one thing other videos explained that this one didn't is that the key fob should be facing down, and that is the only method that worked for me.