A few problems
 

This is probably noobish but, a fair bit of the time when I'm driving my truck and I go to shift gears, the engine revv's up when I pull it out of gear or press the clutch and takes forever to drop at all, let alone down to idle. Huge pain in the ass when I'm trying to drive and it takes 15 seconds to shift gears.

Also, it likes to stall when I stop. It seems to idle fine most of the time but when I slow down, especially quickly, it'll die.

I've tried adjusting the carb a bit to no avail. The mixture screw (tried setting it to 2.5 turns from fully closed as this carb faq suggests and it didn't seem to run very good at all, which direction is which on the screw anyway?) and the low idle don't seem to do much when I touch them (cold/warm, off the fast cam), the fast idle definitely adjusts fine and is set good. Maybe I'm just too baked.

Also, occasionally (though, seemingly less often recently, thankfully too), when I press the brakes, the pedal goes nearly to the floor before applying any pressure, if I let up on it and push it again, it's fine. What could be causing this?

check your brake system for leaks, adequate fluid, and your pads/shoes as well. Is your fuel filter clogged? Pump doing it's job?

I bled my brakes yesterday after taking my rear axle apart. The brakes are much more repsonive now, and the pedal feels nice and solid. It only takes 30 minutes to do all 4 and made a big difference for me.

You can test for air in the lines, start up your truck and push down on the brake pedal. Turn off the truck, and if the pedal holds firm for 10-15 seconds its good, if it starts going to the floor, you have air in the lines.