Hi, All. Long time, no post! Not since I've sold my Challenger in 2014! In any case, I need help with a brake issue on my '87 Dakota.

The truck doesn't get driven much, I've had it 8 years and put 10,000 miles on it in that time. It has been trouble free for 8 years until now. I went out a few weeks ago to take it around the block and noticed that the brake pedal went to the floor. When I started it up, the brake light was on until I pumped it a bit. As I drove around the block, each time I stopped, I had to pump the brakes to make the brake light go out. I assumed the master cylinder had bit the dust so I replaced it. After replacing it, I cannot get the brakes to bleed. Using a vacuum bleeder, no matter how many times I pull a vacuum and crack the bleeder, there's tons of air coming out. I literally spent an hour just on the fronts trying to get the air out. Also, still have the same issue at the pedal. No brake fluid anywhere indicating any leaks and the fluid level was not low when I changed the MC. What am I missing?

Thanks!!