Brakes pedal hard to push down...
 

I ought to have more stopping power, and the pedal is hard to push down. What is the main cause of this?

most likely a leaking brake booster and/ or poor vacuum supply.

Next time before you shut your car down, have your MightyVac handy and tee into the main vac line that runs to the booster - take a reading

disconnect the main line from the booster and plug it well - take a reading.

agree not enough vacuum

or a leak in the booster normally from a leaking master or one that was leaking and they did not remove all the fluid that did leak in -- jz

That's what I thought as I have a vacuum leak I can hear from below the climate controls- I wanted to reaffirm, thanks!

There are a bunch of connectors right by the fuse box/MC (providing vacuum to climate control) that tend to bend and pop off as well so make sure you check there. Had one pop off on me more than once...just 0.02