[dsraven]

we will need some more info
is the brake system all completely stock? drum brakes and single system master cylinder mounted under the floor?
did the master cylinder EVER run dry on fluid when you were bleeding?
have you looked at any of the other brake components, steel lines, rubber hoses, brake shoes, park brake cables and brake adjustments?
are you sure you have a bottle of brake fluid and not something that looks like a brake fluid bottle (don't laugh or get mad, this happens. somebody mistakenly puts a "same brand" bottle of another product, that is packaged in the same color bottle as the brake fluid bottle, on the shelf where the brake fluid is placed. you grab it thinking it is brake fluid and dump it in. that is why the fluid looks murky, because when the brake fluid is mixed with this other product the outcome is murky fluid. I know a guy who filled his master cylinder with diesel fuel additive because somebody had put a bottle of the additive on the shelf where the brake fluid was. the 2 bottles looked the same and were the same color). another reason for murky fluid is water contamination. if there is water in the brake lines for some reason then that would explain it. air bubbles in the fluid can also make the fluid look murky. try to get a sample and see if the murky goes away after the sample sits long enough for the bubbles to find their way out. or keep bleeding until clear fluid comes out at each bleeder hole. start the process by cracking the lines at the master cylinder to bleed the master cylinder ports. then work your way back and bleed at each connection from there to the furthest away wheel, usually the passenger's side rear. then the drivers side rear and so forth. have a friend help you and have him press on the brakes before you crack the fitting or bleeder, then hold the pedal down until you have the bleeder or fitting tight again. then check the fluid level in the master and go to the next bleed location.
if you can't get the bleeder screws to come out then you can also simply loosen the brake line fitting on that cylinder to assist with the bleeding. you really should replace the bleeder screw or the wheel cylinder though. I have found that you spend more time trying to fix the bleeder screw than if you just replace the wheel cylinder right outta the chute.
have you checked the linkage for the brake pedal to ensure the free play is correct and also the linkage is not binding or worn out? I assume the master cylinder cap is new as well as the master cylinder? new, like from the store. not "new to you"?