I'm from Lubbock and did the drive to and from A&M quite often.
Best route I liked was SH 6 through Waco and Eastland; then IH 20 of course from there westward.
Tried SH 36 often through Temple, Abilene, etc, but this route has more small town speed traps and signals.
From Houston, you almost might as well just take IH 45 to Ennis and then use US 287 to cut over to IH 20 in Fort Worth. This way is DEFINITELY more miles, but your average speed will DEFINITELY be higher and the total travel time will probably be less.