Simple stuff first - take out your tire pressure gage and make sure that your tires are up to pressure according to the placard inside the driver's side door.
Once that's done, and you are experiencing the same trouble again, I would inspect each tire on your truck. Are they the same tread depth? Did you replace one, or a pair of tires and are they the same brand/tread type pattern? have you been rotating your tires properly at about the same time you change your oil? (Every 6 months/6000 miles)
Then it gets technical... But we will not talk about that until you got the basics covered first.
