and if you get tired of driving - the Megabus service in TX is nice, especially for the HOU - New Orleans leg.

I'd also suggest Killen's BBQ in Pearland (near Houston) - the best bbq brisket I've ever had - well known nationally. So good!

Final tip, and then my boss wants me to go back to work for THE MAN: Suggest looking at this blog, which has some nice info about US military heritage in SAT:

http://alamocity.citymomsblog.com/20...stinson-field/

AND there is a nice ARMY museum in AUSTIN in a facility known as "Camp Mabry"

http://texasmilitaryforcesmuseum.org/

Since you will be in the Houston area, don't miss Galveston. With three weeks, you have even time to go to Big Bend National Park if you want. Yes, Texas is huge and diverse. If you have that much time, why not sample a little of everything?

Between Houston and San Antonio are the Painted Churches is Shulenberg.

Hill Country are will be beautiful in April. Wimberley, Luckenbach, Fredericksburg, Johnson City - all great stops. Lady Bird Johnson Wildflower Center may be of some interest.

Big Bend definitely!

After several week-long trips, how I WISH had three full weeks to travel 'round Texas! So much to see and enjoy, including its best attraction: Texans! Great, friendly, proud people.
If,in addition to seeing "cities of interest" as mentioned in your original post, you enjoy small towns...I loved the Rockport/Fulton Harbor area. There's a gentle low-key loveliness there. Not spectacular, just very relaxing and great for a day trip or, as we did, a two night stop.

The most beautiful part of driving in western Texas is the sign that says "Welcome to New Mexico ".

Logandog - and the best part of driving back into TX is the Whataburger sign!!