Offroad-Express

Need some help from any brake guru's out there...This one has me stumped.

The playdoh has an intermittent hard brake pedal....But here's the kicker.. when its hard it stops just fine....not like a hard / no booster assist...feel.
I have done the usual brake checks.. Bleed off the booster assist and start truck with brake pedal on... Its drops like its supposed to.
I have no leaks... brakes all bled fine... no binding calipers.
Its quite random...
The only thing I can think of is when I changed the seals in the master cylinder with a kit.....
I measured the rod length in the booster to master cylinder per the manual...Didn't need adjusting.....so I think I got it right...
What symptoms would you get if it was wrong???
Its been thru several wofs like this and has never given the wof man any reason to query it..
Like I said it stops great ....

The only problem I've had with the booster rod was when it was a bit long and it slowly brought the brakes on while driving till they locked up.Had to crack a bleed screw then could carry on for a while again.When shortened a little never had the problem again.If it was a bit short couldn't see it making the pedal hard.I think it would be a problem in your booster,master cyl,pedal area but not sure what.

could you put a tee is the line that goes to the brake bosster then put a line from that to your boost gauge to make sure that it always has negative pressure, or at least when the brakes go hard that it still has negative pressure, one way to rule it out

I think I have fixed the problem, my pedal adjustment didn't have enough free play in it... loosened it a bit and now the pedal feels o.k and doesn't go hard (if only)