OK, sounds like you are not familiar with drum brakes.
First thing I recommend contacting one of the vendors for the "big book" service manual for your truck.
Here is a video that gives a high level over view of your drum brakes, and the visual will help you understand what may be working against you in accomplishing your task.
When I said to make sure your shoes were compressed inwards, I meant that you have to manually adjust them to contract via the star adjuster located at the bottom of the drum section.
Grab a flash light and crawl behind the brake backing plate, at the bottom section look for a rectangular window/hole. Shine your light in there, and look for that knobby wheel. That is what you need to turn to adjust the shoes inward away from the drum surface, a screw driver works but a proper adjusting tool is angled in such a way that makes it easier.
Sears sells a complete drum brake tool kit, so it would be a good investment and make your life a little easier.