I don't run my truck terribly hard but i am in several dusty harsh environments and figure keeping oil and air filters changed regularly is cheap insurance.

 

I'll change my air filter and cabin filter once a year. Averaging 50k miles +/- a year in off road dusty conditions, never seen them where I thought they should of been changed sooner.

 

I'm never in a hurry to change air filters. Dirty Air filter will filter smaller micron than a clean filter. So let's just say an air filter has a 30 micron rating, when it's dirty (not plugged) it could be filtering 25 micron and actually be doing a better job. I have no idea what an actual air filter micron rating is so I just picked number for an example.

the key is to not adversity affect air flow/performance. I like to use a light to see how well light filters thru the filter. My every day vehicle has 90,000 miles and it's still getting great fuel mileage, so I'll keep on running it.