Took this straight from the DPS website:Texas DPS Inspection Program
What's Inspected by Vehicle Type
Items of Inspection
05.02 Inspect Every Pickup, Panel, or Truck Under 80 Inches Wide For: (Listed in suggested order of inspection)
* Check for evidence of Financial Responsibility
2. Windshield Wipers
5. Seat Belts
6. Brakes (system) Parking - (beginning with 1960 models)
8. Wheel Assembly
9. Safety Guards or Flaps (if four tires or more on rearmost axle)
10. Exhaust System
11. Exhaust Emission System (beginning with 1968 models)
12. Beam Indicator (beginning with 1948 models)
13. Tail Lamps (2); (1) if 1959 model or earlier
14. Stop Lamps (2); (1) if 1959 model or earlier
15. License Plate Lamp (1)
16. Rear Red Reflectors (2)
17. Turn Signal Lamps (beginning with 1960 models) (mea-sure if 1959 model or earlier)
18. Head Lamps (2)
19. Motor, Serial, or Vehicle Identification Number
20. 1988 & newer - inspect for window tinting or coating
21. Gas caps on vehicles 2-24 model years old.
Overall width is determined by measuring from the widest part on one side to the widest part on the other side of the vehicle. In some vehicles this may be the dual wheels which would be considered as part of the width. Do not include an outside mirror or mirrors in determining overall width.
As with most such things, you are just taking your chances by altering the emissions system. 99.9% of cops probably wouldnt care if you didn't have a muffler or a cat unless it was annoyingly loud or smoking or some such thing. But there is always that 0.01% who are anal or just have a chip on their shoulder that will write you up just because they can.