Josh,
I have seen the flexible line swollen and plugged, t-block connectors plugged, and wheel cylinders corroded to heck. These parts are cheap enough at your local parts stores, and easy enough to replace, that I would replace the wheel cylinders, flexible lines and steel lines. Check the t-block to make sure it is clear too. Get the stopping power fixed and safe the first time. Let us know what you find.
P.S. Just because the fronts work, doesn't mean they don't need some service. Remember how old your truck is, and I will make an assumption that it has probably sat for some time too.
