Sorry for asking the same questions in different ways, but we're trying to help figure out everything that may contribute to the situation. Now bear with me while I think through this.
1. If you have to pump the pedal to get resistance, one of the following is the case:
a- there is air in the brake line.
b- there is excessive clearance between shoes and drum or pad and rotor.
I know you said you bled the brakes 3 times, and you had good pedal pressure. and you also bled the LSPV.
I am leaning more towards b- in that the internal linkage may have gotten misaligned and the starwheel adjuster may have come out of place, leaving nothing to keep the piston from popping out of the cyl. But this is just speculation. When you take the drum off, would it be possible to take a pic and post it? This has got me
.
The adjuster problem i just mentioned happened to my wife's car. The adjuster wasn't functioning (it's an auto trans and she doesn't use the e-brake, so, no adjustment), and the pedal went further and further. then one day she got home and told me it was grinding really bad. i pulled the drum off, and the starwheel had fallen out of place and was grinding against the side of the drum.
But, like I said, it will all be speculation until you open it back up and see what has happened. Then, we can better figure out WHY.
P.S. aren't there two drum sizes for toy rear axles? I'm not sure, but when i redid the rears on my 2wd, i seem to remember them asking me which i had. maybe they gave you the wrong ones (brake shoes or drums - you didn't say if the drums were new, or just in new shape)? shot in the dark, but worth asking.