Brakes are stiff while driving.

Brake Fluid levels are fine. Haven't done anything to my truck in months.

The problem seemed to have gone away over the last 2 days, so I'm not sure wtf it could be.

 

I wouldn't play around when it comes to your brakes. you could get yourself or someone else injured or worse. If you can't find an obvious problem, take it to a good repair shop and get them to take a look. SOMETHING was wrong.

 

Just got back from mudding/offroading. Brakes seemed perfectly fine.

Is it possible maybe something was clogging the vacuum to the BB?

 

Hmmmm. For the last 2 days this problem has sporadically been reoccurring. For clarity, the feeling doesn't feel like my Brake Booster isn't assisting me. It feels more like I have air pressure in my brakes that's working against me when I press it.

 

have you tried bleeding the lines as a simple beginning point?

 

Yep.

 

update on what the problem was?

 

If your brake pedal slowly bleeds off with light foot pressure, I believe it's the master cylinder I've had this problem before on other vehicles.