what year truck ? after 70 ? or before 70 ? front or rear ?
if a drum is grabbing bad and maybe evne locking up then it might bne fluid soaked into brake shoes material, leaking wheel cylinder or axle seal
if its a front drum doing it then its probably cuz the both fronts are not adjusted out to close enough to the same so that one is braking before the other, and that is what would cause a bad pull to one side when braking
its pretty straightforward ot take apart drum brakes, you just need pliers to take apart rears,
if are fronts then you need tools to unbolt the hubs that the drums ride on
most of the time you have ot back off the shoes so that the drum will evne slid eoff the shoes, this is the real fun part, and alot of the times none of the adjustment access knockouts are knocked out and open, so you have to find them, sometimes they are on the face of the drum and sometimes they are just in the backplate, or both.