Brake Pedal

97 5.0 k1500
When I step on the brakes there is a squeak at
the brake pedal - almost a whistle and I can
feel a slight breeze on my foot. Also, while stopped
and holding the brake for a while, I can feel
a little pressure fade and the pedal will sink a bit.
I'm not sure if this just started or I just started
to notice.
So far replaced leaky wheel cylinders, front pads & rotors, bled
Thanks for any thoughts, I'll search the forum in the meantime.

Sounds to me like the diaphram in the power booster sprung a leak. Time to replace the booster.

//2000CAYukon

Thanks for the reply. I found instr. for replacement
and seems straight forward. It looks like the part
is a little over a hundred. Is there a way to diagnose
the booster? I looked at the vacuum line to it and
it seems OK. Could the check valve cause a prob.?
Thanks again