A few things to consider based on what Cyclopathic mentions above:

Sam changed the route which cuts diagonally across Nevada from Baker to Denio for a number of reasons - not that it is 'too hard' per se, rather than if you are riding Colorado during July when the snow ought to be gone, then it can be hellishly hot in Nevada end of July/August, plus there is a lot of sand which riders on larger (and overloaded) bikes are likely to struggle with, particularly since they will have been on the road already for three weeks or so.

There are also issues these days with Sam's original Nevada route due to mining operations (I rode this original section again in 2020), plus, when he made the major changes in 2015, it was because Denio Junction (the only fuel for 160 miles) was no longer selling fuel...

Subsequently however, Denio Junction is now trading again for fuel (and food and a small motel) so it is viable to go that route if you wish, as long as you're aware that parts are very remote, and there are a number of soft sandy sections - so choose your bike/luggage accordingly.

Similarly, as Cyclopathic mentions above - GPS Kevin's 'hard' routes in places are very much suited to more experienced riders for smaller dual-sport style bikes rather than heffers like the KLR and larger twin-cylinder 'adventure' bikes which a lot of people these days end up riding the TAT on - which is why I suspect Sam changed his route over the years to make the trip more manageable for these riders (he knows his audience) - again, as I suggested previously, I would get both routes and use those to plan your own cross-country TAT, based on your own experience and what kind of bike you plan to ride.

Don't forget there are no prizes for riding either of these TAT routes, they are just a guide which link together a series of good unpaved roads and trails across the country, and pass by a few interesting places to visit. Also be honest with yourself what you actually want out of the trip - and if that is to finish, and not have to bail out early because of damage, fatigue or injury, then plot your own route accordingly.

Personally, unless you absolutely want to say you've ridden from coast to coast, then from an off-road perspective the 'good stuff' really starts once you get to Colorado and west, so it's perfectly feasible to plot a triangular route on the west side of the US which uses Kevin's southern Spur and Sam's Northern/main route (which goes via Idaho into Oregon) and then back down south via the California BDR route to get the best of both...

However if you do want to ride coast to coast, then for foreign visitors at least, I'd agree with Cyclo' and perhaps consider starting in New York (if you want to visit there) and head south for Virginia and perhaps take in parts of the Blue Ridge Parkway and the Mid Atlantic BDR route (which is basically the same Route Sam now follows through his Virginia section, since there really is only one main through-route on dirt in this area), and continue on his TAT in North Carolina (you go close to Asheville, and also the Tail-of-the Dragon on the Tennessee border).

If you are starting earlier in the year (and have plenty of time) then it's worth continuing west on his TAT route if you want to do the tourist thing - you're not far from both the Jack Daniel's distillery and also Memphis if you want to visit Graceland for example - but other than the odd section in Arkansas, you're probably better off streamlining through Oklahoma and pick up the TAT 'proper' once you get to Boise City OK in the west end of the Panhandle, and dip into New Mexico before you reach Trinidad CO, which you can the plot a through route using either Sam or Kevin's tracks (plus I would suggest a side trip up to Cripple Creek and Pikes Peak near Colorado Springs) depending on the bike you've chosen and how much of a 'challenge' you're looking for.

fwiw. Personally I would follow the Engineer, California and Corkscrew Pass (Sam's route), then head down Hwy 550 to Ouray and go over Imogene Pass to Telluride - however, there is one spot on the east side of Imogene which is very steep and loose and tough on a big bike unless you are very committed.

I'd suggest that Ophir Pass is the least impressive of all the crossings there, and certainly heading west and down the tailings, ought not to prove too much of a challenge for a larger bike - although personally, I'd suggest you turn left after you join the highway 550 from Corkscrew Pass and ride the 'Million Dollar Highway' south to Silverton, and then continue down to the Purgatory Ski resort (and even visit Durango a few miles further south, especially if you like steam trains!) and take Hayden pass across the mountains, and rejoin the original TAT route on the far side.

As for Sam's 2015/18 reroute in western Utah, it's worth the visit to Bonnieville - particularly as at that time of year there ought to be some speed-week testing going on (as long as the lake is dry), and Promontory Summit (where the trans-continental railroad joined) is also worth seven of your tourist dollars.

Also, Sam's Idaho route via Arco, Ketchum and Featherville (with a side trip up to Trinity Mountain) is definitely recommended, and then personally speaking I would do what I did back in 2015 (before Sam had plotted his route though the middle of Oregon), and head south west from Boise/Mountain Home along the old ION trail to Denio Junction in Northern Nevada, and then ride Kevin/Sam's original route from there all the way to the Oregon Coast.

Hope that gives you something to go on - as I say, you're not going to be able to follow either route 'inch perfect' anyway, so you might as well get both and together with a couple of the BDR maps too, spend some time and custom build your own 'TAT' which takes in as much of what you might want to see, and provides as much or as little of a technical challenge as you feel prudent.

Jx