A small or midsized truck crew and some extended cabs can fit 4 comfortably and can fit 5-6 uncomfortably. Anything but a full sized truck is too narrow to fit 3 people side by side comfortably.
_________________________
https://connect.garmin.com/modern/profile/eugenenine
https://pixelfed.social/i/web/profile/587437729469961861
https://www.alltrails.com/members/eugenenine/recordings