Thanks for the replies so far, guys.
litew8: I did all of those things, and then I did them all again -- some more than others. Got a few bubbles out of the MC the second time around, so I bled the snot out of it. It's good now, for sure. Only thing you wrote that I couldn't do was 'repeat until air bubbles are gone'.
68gmsee, I didn't replace the rear hose yet simply because I'm already over budget and it's a spendy little devil. I may bite the bullet and do it anyway. Those connections have not been touched, probably since the truck was built, and there's no sign of leaks.
Your idea of isolating the problem gave me another thought. Since I have a hard pedal with the rear line off of the MC, I'm going to try disconnecting the rear line from the prop. valve to make sure it's good. Maybe I can find other connections to cap off and pinpoint the problem.
I haven't given up yet -- I'm determined to fix this bugger without taking it to a shop.