it depends more on how you drive your truck than how long or how many miles. if you use your rig for short hops around town or in dusty/dirty conditions, more frequent oil changes are called for. if you get the motor up to operating temps for long periods of time and it sees mostly highway miles, extended oil changes may be fine. the heat will boil the condensation out of the crankcase.
Guns don't kill people, drivers with cell phones kill people.
