Hidden gems are where you find them.
A fallacy is that somewhere there is a list of hidden gems. Once a place is mentioned in a guide book or on the internet, it ceases to be a hidden gem. It will be widely known to all qho read these published words.
Hidden gems are those things you find by sheer chance, by getting off the high speed highways and wandering the backroads, by speaking with the locals in any locality, and asking what their favourite spots are.
Even if I knew of any along your intended route, and I were to mention them here, they would cease to be hidden gems. The tens of thousands of folk who visit this site every day would be aware of it.
Lifey
Why not fulfill both your wishes in one.
As mentioned, get the maps and do your research. Absolutely no need to go to Texas for gunshops, you will find them abundantly in most States, especially the western States. Thing is, you will not find the spectacular national parks in Texas. The best known and most visited ones are in California - Yosemite, Sequoia,. Death Valley, etc.; Utah - Zion Bryce, Arches, Canyonlands, and more; Arizona - Grand Canyon and others.
So look for spots which fulfill the wishes of both of you. Once you have your maps, and do your research, you will no doubt come up with much more The maps will also show you the many many routes you have to choose from when you head out of NYC to the west/southwest. You will note that besides the high speed interstates, there are secondary highways and lots of local roads. As well as all that, scenic routes are highlighted,
There will always be someone here to help refine your route and fill in the gaps. So as Dave said, once you have some dots on the maps, ask away.
Lifey