Redcorn Gambles with His Future - S9-E11
Other mistake: In the season four episode "Nancy Boys", when Nancy calls John Redcorn and tells him that she wants him back, he says, "I'm thirty-six years old. I don't need this crap." But here while John is talking to Hank, he mentions waking up one day and realizing that he is forty. If four years had passed since his break-up with Nancy, then Bobby and Joseph would now be sixteen and at least sophomores in high school, but they are still in middle school.
Answer: Jeffrey Boomhauer is a Texas Ranger as can be seen in the final episode at the end when he sets his wallet down, it flips open revealing a Texas Ranger badge.