lucky7matt,
1953 3/4 ton Chevrolet truck?
There are adjustments that can be made:
door adjustment (locate the door in the center of the cab opening)
then
door striker plate adjustment (in/out and up/down) - if these parts are significantly worn, a seemingly tightly latched door can slip out and rattle.
Is there significant wear on the contact surfaces on the striker plate and/or on the door lock/latch?
With you doors open, how tight are your hinges/hinge-pins (up and down movement of the door? (loose hinges cause significant rattling and can allow the latch/catch to loosen).
What is the condition of the door seal? (on/around the door). If all mechanical parts are tight, the seal is really a draft-seal, not an anti-rattle seal. However, a good/tight door seal will lessen rattle and maybe lessen door movement when you have other loose parts.
In a stripped-down restoration, before installing the door seal, we try to set up tight doors that cannot be moved/rattled when closed (with no seals in place).