Bad brakes 97 dodg ram 4x4 360 RWAL brakes

Hi all
I have a 97 dodge ram 4x4 with rwal brakes, they feel ok when
stopping normal , but in a fast or sudden stop
where you press harder on the petal they seem to run out of reserve
booster petal from this point on you need two feet to stop the truck,
but it still dosent stop fast, you would have a hard time locking the
brakes up in the rain. (rwal disconected for this test)
I checked out the power booster per service manual and passed all test
(still vacume after 24 hrs for 2 petal pushes)
The brakes were blead in proper order, brake shoes were ok and proper
clearence was checked. cleaned and checked brake pads , they were ok
I replaced the master cylinder and bled it the proper way (had a extra
new one)
both the brake and yellow rwal light come on once in a while but go
out when they feel like it.
I had driven the truck with the rwal disconected again , this isnt
helping at all in a sudden stop.
Could the nitrogen charged rear hydrolic control unit lost some
pressure or lost its charge altogther
And causing the brake fluid to migrate up into the valve body, It kind
of works like a bladder for a well pump
but is controled to pulsate ,depending on feed back from the sensor in
the rear end , how fast the weels are spining What about the
combination valve? could that be defective.
Like i said the system has no air or any type of gas in the lines,but
the petal feels like it when stopping fast