Okay, with that out of the way, just a random thought. Does it have to be the Trans Am? You could ride the eastern Trans Am and then pick up the Route 66 or even drop down to the Southern Tier.
FWIW, I didn't find that the ST had much going for it other than that 1- it can be ridden in winter, 2- it is the easiest way over than the mountains, and 3- the food and people were interesting, Still the scenery was pretty uninspiring most of the way and there were day after day of endless dry brown sagebrush punctuated by nothing. Maybe you'd miss the most boring parts depending on where you headed south, but why? Much better to just do the TA W-E.
Riddle me this, fellow forum denizens: raise your hand if you know why the Trans Am takes a ~400 mile detour north to Missoula. Anyone? Bueller? Bueller?
Because Adventure Cycling is headquartered there? To be fair it was a pretty nice section and probably better than the shorter route. I really enjoyed that section it has some of the best memories of the trip. We met some nice folks who hosted us in a couple places, we went rafting on the Salmon, we rode along the beautiful Lochsa river up to Lolo pass and enjoyed Jerry Johnson Hot Springs on the way up, we saw a herd of bighorn sheep, Big Hole Battlefield was a great stop, we spent the 4th of July with a group of motorcyclists who gathered in Jackson Hot Springs, and while it wasn't there yet for us there is now a nice bike camp in Twin Bridges (we stayed in the fairgrounds).