Parking brake dosnt hold vehicle

i am not you but so of these truck has small dics behind the rotor and that your parking brakes and they may need to be replace give these websites a try www.alldatadiy.com and www.autozone.com if all fails stop by your local library and get your hands on a Haynes auto manual for your car i also would like to give you this information if you every have any hard to find GM-parts its Schram auto & truck parts 1-800-292-1032 and they website is www.schramauto.com wish you the best of luck Michigan man.

Rear brakes can be adjusted to compensate for wear , and brake cable can be tightened to compensate for stretch. More likely that your rear brake linings are just worn to the point that the park brake mechanism doesn't open them up enough.
Take it to one of those chain brake places that offers a free inspection. If it just needs an adjustment , they might do it during the inspection.

Underneath the vehicle is a turnbuckle to tighten the cable for the parking brake you need to turn it until his tight enough that when you engage your parking brake it will function properly.

Parking brakes may need to be replaced or adjusted.