pressure bleed the system

if thats not possible then you'll have to bench bleed the master cylinder first (if you didnt do it the first time)
the angle these mastercylinders are mounted at makes it extremely hard to bleed them as they tend to form a bubble of air in the high side and it is hard to get that air out. Even after bench bleeding they still tend to get that air pocket in there and you wind up having to bleed it on the truck through the lines and it takes several times and alot of fluid.

as for the wheel cylinders, check the wheels at the backingplates underneath the truck, if you have fluid present on the wheels then the wheel cylinders are leaking, if no fluid present then they are probably ok. You can pull the wheels just to be sure but if no fluid on the shoes then they are ok.
while u have the wheel off you can rough up the shoes and even drums to help shoe gripping ability, glazed over shoes or drums that are not properly seated can cause poor brake performance.

make sure the wheel adjusters are in good order and adjusted up as far as you can get them without causing too much drag on the shoes. You may have to adjust them, operate the brakes in fwd and rev some and then go back and readjust after the shoes settle in place.

Ultimately if the only problem was a leaking mastercylinder and you just had to replace it, or excessive pedal travel then i would say its just getting the air out of the system and proper wheel and pedal adjustment.

The pedal adjustment is usually a simple process of adjusting the rod between the plunger in the mastercylinder and the pedal yokelink. It should be no more than a 1/2in movement in the pedal before it contacts the plunger and starts to push on the plunger in the mastercylinder.

Also if you happened to have adjusted on the course adjustment bolts for the pedal height, go back and put it back where it was, pedal measurement from the floorplate to the pedal height should be no more than 8in from floor to top of pedal pad. (note: the inching pedal should be even with the brake pedal but donot try to adjust this till after you get the brake pedal adjusted, and once you get the inching pedal set recheck the inching linkage and make sure the cable is set so the linkage is not pulling the cable and pushing the spool, also you can use the brake mounting bracket as a base point for measuring since the floor plate is supported by this bracket.)

Brake fluid for these trucks is the standard DOT3 brakefluid in case there is any question on what fluid to use.