2007 Brake Booster and dash lights

Hello, I have a 2007 Toyota tundra 5.7 l 4 wheel drive. I'm having an issue with the brakes. Sometimes when going down a hill the brakes will get stiff. ( The pedal will get hard to push) Then if I push it harder, The brakes lock up and make a vibration and then the brake light comes on, VSC light and traction control light on the dash. I have come to understand that it could be a problem with the vacuum hose that might have a leak in it that goes into the brake booster. Or it could be the brake booster itself? How can I know whether it's the line that goes to the brake booster or the brake booster itself? And question 2: Why would those 3 lights come on? What could the brakes or the brake booster being messed up Have anything to do with the dash lights? Then when I turn the truck off and back on again the lights go away and the brakes go back to normal. Let me know what you think, thank you .

 

No I haven't flushed the brake fluid Ever since I got the truck 2 years ago. Brake fluid level is good,I recently replaced all 8 brake pads