Technical Overheating engine and stiff brakes at the same time

So I've been adjusting for a week and driving it around. The brakes seem to change each time, sometimes they great. other times the pedal goes to the floor and I hope to stop. When idling at times I can pump the brakes and they build up pressure but then lose it when in gear. And again other times when idling and when pumping the brakes no pressure builds up. I'm going to borrow a vacuum gauge from a friend to see what I'm pulling from the intake manifold where the vacuum line is connected.

I saw, maybe on this site, a discussion on whether adding a vacuum canister when you're pulling low vacuum helps or hurts.

Sheep Dip - others also pointed to heat issues, there's no exhaust by the booster, but I'm sure it get's warm under there but nothing more than if the booster was under the hood in the engine compartment. I wonder at what temp would the booster start to be affected?

 

I also just did the following for testing the booster, before dropping $150 for a new one.
I've done the first one in the past but not really 2 or 3 before. I got these from Roadkill customs site.
Power Brake Booster Test 1 _ P***ed, the pedal did drop by about 1/4"

1. With the engine off, pump the brake pedal to remove any residual vacuum in the booster.
2. Hold pressure on the pedal while you start the engine. When the engine starts, the pedal should drop about a 1/4″, this indicates that the booster is working properly.

Power Brake Booster Test 2 _ Not p***ed the pedal did not get firmer afterwards

1. Run the engine a couple of minutes.
2. Turn the engine off and press the pedal several times slowly. The first pump should be fairly low. The second and third should become slightly firmer. This indicates an airtight booster.

Power Brake Booster Test 3 _ P***ed, the pedal didn't drop

1. Start the engine and press the brake pedal, then stop the engine with the pedal still pressed. If the pedal does not drop after holding the pressure on the pedal for 30 seconds, the booster is airtight

 

If you have a pedal that goes to the stop for no reason, the master can be byp***ing internally. Give it another pump and the pedal is back on top. Try to replicate the dropping pedal, at home in the driveway. Engine off it may do it, but with power brakes try it running. Tickle the pedal, moderate pressure, bounce off and on the pedal lightly. Then a little harder. It may do it when you drop the car in gear with a foot on the pedal.