2001 Ford Expedition Losing brake pedal pressure

Brake pedal seems to be engaging a little lower than normal. Truck stops fine however if at a stop light the pedal slowly starts to drop and the truck creeps forward unless you apply additional pressure on the pedal. Fluid level is good and has not dropped

I have:
Replaced the MC (rebuilt from OReilly)
Bled the brakes several times (new fluid coming out in solid stream)
Checked for leaks at the wheels (none noticed)
Checked the vacuum line to the booster (good vacuum)
Checked the one way valve on the booster (only allows single flow)
Just replaced rear pads (even though old pads were at 25%

With the truck off the pedal pumps up hard. But will slowly lower with constant pressure on the pedal. If I start the truck after pumping it up the pedal drops quickly