all new system/bad brakes

[willysz28]

Hello all,
I recently upgraded to later 3/4 diffs on my 68 sub. I also added power brakes at the same time, using tuff stuffs kit, and a wilwood prop valve. I have bled out the system, but have a hard pedal and ****ty brakes. They are better in reverse actually... but still suck.

I have trouble shot and the vac canister holds air after I shut down, I'm getting 20in vac at idle, and the pedal drops when I start it. Tuff stuff's booster is a 11" single diaphragm, and is universal for 67-72's with a bracket that addresses the "rod issue." I see that the 73-87 trucks were dual diaphragm though... Is this my issue? Shouldn't an 11" single still have good stopping power?

Any help is greatly appreciated!