take 10 to 290 to 35. 35 will take you straight into killeen.. and if you keep going, ft. hood. used to drive up (through) there all the time. admittedly, it's killen, so i never did stop. you might get caught behind a 35mph convoy between austin and ft. hood, but they know what a headache that is and usually let you pass.
(god... get off of 10 as soon as you can in houston. time it so that you don't hit rush hour.)
gas in houston is ~2.89 regular unleaded right now. plan to pay more since you'll be right on the freeways.