easy check. jack up the truck. make sure tire is off the ground but still have lugs tight. if you can wobble the wheel then they need replaced.
you change them when they start to go bad. if they are,t bad then leave them be.
If its making noise, do it now. If not just clean them with solvent, and repack them. Do like the manual says to do.
There is no specific schedule for changing wheel bearings on anything. You should check them periodically for excessive play, but that`s about it. You can do this by jacking the wheel up and using a pry bar to check for excessive movement in the wheel. If it is fairly snug, but noisy, just re-pack the bearing with proper bearing grease, If it feels loose (a little is normal) then replace the bearing.
Most wheel bearings will last 75k. mile and more if they are properly repacked during each break replacement. If they have not been done during any break replacements. Have them looked at. Do not use any type of pry bars to check for movement. There are several parts on a front end that can be damaged by this method. If you think you are having problems with the bearings have them checked.
