Lenard
Double check all your adjustments and fix the leak first.
I know you bench bled, but try this also...
rebleed the master on the truck at the inlet AND outlet side of your new valve sometimes a SMALL amount of air in the valve itself will cause wierd problems. Then standard bleed pattern starting with the longest line first. Get a helper and do not push more 1/2 way down on the brake pedal, close off the valve while it still has pressure.
I had a 88 pu that drove me nuts one time, similar problem m/c & rear brakes = major headache. air and a rear drum that did not seat right and had to be readjusted.
