55.2-59 Brake issues

[2bo.c10]

Hi Everyone -

Background: I installed a new master cylinder about a month ago and attempted to bleed the brakes immediately after installing it.
Back right: Bled Great!
Back left: Bleeder is screw was stripped
Front right: Bled when it was first cracked open, but then that was it! Every time I would try to bleed them after that nothing would come out.
Front left: Bled fine, but the fluid seemed murky. This is weird considering it should have all new fluid running through the lines. I bled it about 5 or 6 times but kept getting the murky brake fluid.

Before doing any of this there was NO pressure in the pedal and after doing the above I had great pressure in the pedal. I have drum brakes all around.

Moving forward...

The Issue:Yesterday I take my truck out of the garage for the first time since I bought it - Thought I could make her maiden voyage a VERY short trip (not even 1/2 mile away) to my mother's for christmas. Didnt work out that way... As I drove it up the street, when I would brake, it would seem fine (didnt pull to one side or anything like that) but as the truck would come to a stop from braking, it seemed like one of the wheels was locking up. It wouldnt happen right away when the brake was applied but as the truck was finally coming to a stop.

Based on what I've described, anyone have any idea on what it could be? Any and all help is very much appreciated!! Thank you!