Where in Texas to where in Michigan?
Assuming something like Laredo to Detroit, your options range from north on I-35 to I-80, then east on 80/90/94 (your choices) to taking something up to I-10, I-10 east to I-75, then north on I-75. That makes a rectangle, and all of the Interstates, U.S. numbered highways, and many of the state highways inside that rectangle are viable options. My own rectangle is Tulsa - Detroit, about a quarter the area, and I've not yet managed to explore it all.
35 years of traveling this smaller rectangle 2-8 times a year, Tulsa and Detroit at the opposite corners, I've found at least a hundred different routes, and which ones I take depends on time of year, how much time I want to allow, who I want to visit enroute, what I might want to see.
I've taken I-40 to Nashville, up to Louisville, Cincinnati, across to Canton, then up to Detroit. On the other perimeter, I've gone north on I-35 to Des Moines, then across I-80 to Chicago, where I might take I-94 across southern Michigan, or the Indiana Toll Road to US-69, or the Ohio Turnpike to I-75.
I've taken US-24 from Hannibal to Toledo, and often take it from I-57 to I-69, though I might detour up US-31 into RV country if I want to visit one of the manufacturing plants in the broad area between Elkhart and Fort Wayne, or visit the RV Hall of Fame.
Depending on time, I might follow the Interstates that replaced Route 66 (by far the quickest route OKC or Tulsa to Chicago area), or that route as far as St Louis and then I-70 to Indianapolis for I-69 to I-94 or I-70 on to I-75 to go north (particularly if I want to visit Dayton again).
Off season for Lake of the Ozarks, I'll take US-54 from Fort Scott to just south of Hannibal, then I-74 to connect with I-55 at Springfield or I-57 at Champaign-Urbana, with options to connect with I-80, US-24, or to run across state highways in northern Illinois and Indiana, connecting with I-94 at Michigan City or working across to I-69. But I seldom use this route to come back from Michigan, because the timing is all wrong for hitting the cities on the route, so from Springfield, Illinois I'll go to Hannibal instead of St Louis, taking US-36 across central Missouri for an overnight 1 to 2 hours outside Kansas City, getting me into KC at the end of rush hour, then I am counter-flow to the commuter traffic on I-35 in eastern Kansas. Every couple of years or so, I'll go on across US-36 to St Joseph, and make a pilgrimage to the Amelia Earhart home in Atchison.
I've also traveled across southern Missouri on US-60, and across northern Arkansas on US-412, to connect with I-55, or to work my way through southern Illinois, or to go on across to Louisville and then either up I-65/69 or on to Cincinnati and up I-75.
Most perverse trip I've taken to Detroit from the southwest has been I-35 all the way to Duluth, across US-2 to I-75, then down from the Soo to Detroit. That one included a side trip to the Little House in the Woods, SW corner of Minnesota. But we were visiting Duluth, the western U.P. and south shore of Superior, so there was a touring purpose. If going into Minnesota on I-35 I will more often divert through northern Wisconsin to follow the Lake Michigan shore in the Upper Peninsula.
Your choices are limitless. There are thousands of interesting places in the middle of the country you haven't seen, if you always take the same route. I'll guess you've never visited the giant ketchup bottle in Collinsville, the courthouse in Nevada, Missouri, or maybe never seen Mark Twain's home in Hannibal?
