[familyguy]

I have never had any personal experience with a problem like this, but I'm copying and pasting the following from my service manual for you (if you don't have a manual). There's also a section on diagnosis of the hydroboost if you suspect that:

Brake Drag
Brake drag occurs when the lining is in constant contact with
the rotor. Drag can occur at one wheel, all wheels, fronts only,
or rears only. It is a product of incomplete brakeshoe release.
Drag can be minor or severe enough to overheat the linings,
and rotors.
Brake drag also has a direct effect on fuel economy. If undetected,
minor brake drag can be misdiagnosed as an engine or
transmission/torque converter problem.
Minor drag will usually cause slight surface glazing of the lining.
It can also generate hard spots in rotors from the overheatcool
down process. In most cases, the rotors, wheels and tires
are quite warm to the touch after the vehicle is stopped.
Severe drag can char the brake lining all the way through. It
can also distort and score rotors to the point of needing replacement.
The wheels, tires and brake components will be extremely
hot. In severe cases, the lining may generate smoke as
it chars from overheating.
Some common causes of brake drag are:
? seized or sticking caliper piston
? caliper binding on bushings or pin slides
? incorrect length caliper mounting bolts (too long)
? loose caliper mounting bracket
? misassembled components
? misadjusted brakelight switch
? binding brake pedal
? master cylinder/hydroboost internal fault
? improperly adjusted parking brake
If brake drag occurs at all wheels, the problem may be related
to a blocked master cylinder compensator port or faulty hydroboost.
An improperly mounted or adjusted brakelight switch can prevent
full brake pedal return. The result will be the same as if
the cylinder compensator ports are blocked. In this case, the
brakes would be partially applied all the time causing drag.