What's the fastest route from SLC, UT to Houston, TX?

I would think that because the Interstate system is supposed to be straighter and with a gentler slope than the US Highway system, your best bet would be to go Interstate as much of the way as is possible. On maps.google.com, I found this route:

Salt Lake City, UT

1. Head west on 400 South/W University Blvd toward S Main St 0.2 mi

2. Turn left onto W Temple 0.2 mi

3. Take the 1st right onto W 500 S 0.6 mi

4. Merge onto I-15 S/I-80 E via the ramp to Las Vegas/Cheyenne 2.7 mi

5. Keep right to continue on I-80 E, follow signs for Cheyenne/Interstate 80

Entering Wyoming 433 mi

6. Take exit 359A for Interstate 25 S/U.S. 87 S toward Denver 0.5 mi

7. Merge onto I-25 S/US-87 S

Entering Colorado 63.4 mi

8. Make a U-turn 15.9 mi

9. Take exit 228 toward Limon

Toll road 1.0 mi

10. Merge onto E-470 S

Toll road 24.6 mi

11. Take exit 20 for Smith Rd toward I-70/Aurora/Denver/Limon/Gun Club Rd

Toll road 0.7 mi

12. Continue straight 0.2 mi

13. Turn left to merge onto I-70 E

Entering Kansas 410 mi

14. Take exit 250A to merge onto I-135 S/US-81 S toward Wichita Continue to follow I-135 S

Partial toll road 95.9 mi

15. Keep right at the fork, follow signs for I-35 S/Oklahoma City/Kansas Turnpike and merge onto I-35 S/Kansas Turnpike Continue to follow I-35 S

Partial toll road

Entering Oklahoma 145 mi

16. Keep left to stay on I-35 S, follow signs for Okla. City/Dallas 6.6 mi

17. Take the exit on the left onto I-35 S/US-62 W toward Dallas Continue to follow I-35 S

Entering Texas 164 mi

18. Keep left to continue on I-35E S, follow signs for Interstate 35E S/Dallas 39.8 mi

19. Take exit 428A on the left to merge onto I-30 E toward Texarkana 1.3 mi

20. Take exit 46 for I-45 S toward Houston 0.8 mi

21. Merge onto I-45 N S 237 mi

22. Take exit 47C on the left to merge onto McKinney St 0.3 mi

Houston, TX

None available, you have to cross at least two state borders.