From the factory, the 1982-1988 G-bodies came with LOW drag calipers and a step bore master cylinder. LOW drag caliper retract the piston into the bore a little further than a normal caliper. This is done with a beveled piston seal.
Rebuilt calipers, from what I can tell, are rebuilt to NON low drag or normal specs as the part numbers for these calipers are all the same from 1978-2004. A NON low drag, or normal calipers, uses a square faced piston seal that does not retract the piston into the bore as far as a LOW drag caliper.
A rebuilt, NON low drag, or normal caliper will work with any master cylinder. A LOW drag caliper can only work with a step bore master cylinder. If you put a LOW drag caliper on a car with strait bore master cylinder, you car will have a long, low pedal stroke and it may run out of pedal stroke before the car can stop.
A step bore master cylinder has two bores for the front brakes only. It has a larger bore initially that provides the volume needed to get the front LOW drag caliper's piston and pads back up against rotors. This bore then transitions down to a smaller bore to provide the line pressure and clamping forces on pads and rotors to stop the car.
Maybe, if you use NON low drag calipers on a 1982-1988 G-body with a step bore master cylinder, you might run into the situation you just described. The step bore master cylinder is supplying more volume than the NON low drag caliper needs initially, so when the step bore master cylinder's large bore transitions down to the smaller bore, it applies a lot of pressure suddenly giving you the touchy brakes you describe.
I would suggest a strait bore master cylinder to remedy the issue. A newer master cylinder option is a RIGHT HAND drive, 2000 S-10. Part number is RAYBESTOS MC390572. This master cylinder has a 1.0" bore and the correct outlets sizes to work with your brake line fittings.
NOTE: A normal, LEFT hand drive S-10, has the 1.0" bore, but the outlets are on the passenger side of the master cylinder and the rear brake port is different than what came stock on the 1978-1988 G-Bodies. DO NOT USE THIS MASTER CYLINDER unless you want to replumb your lines.
You can also go with a 1978-1981 24mm bore master cylinder, but these are usually cast iron and unreliable.
All the years below used the same calipers and all the part numbers are the same for these years for these calipers.
1978-1981 "G-Bodies" came from the factory with NON low drag, or normal calipers and a 24mm strait bore master cylinder.
1982-1988 G-Bodies came from the factory with LOW drag calipers and a 24mm/36mm step bore master cylinder.
1982-1992 F-Bodies came from the factory with LOW drag calipers and a 24mm/36mm step bore master cylinder.
1982-1997 2WD S-10 Trucks and Blazers came from the factory with LOW drag calipers and a 24mm/36mm step bore master cylinder.
1998-2004 S-10 Trucks and Blazers came from the factory with NON low drag, or normal calipers and a 1.0" strait bore master cylinder.
1978-1981 - NON low drag, normal calipers and strait bore master cylinder.
1982-1997 - LOW drag calipers and step bore master cylinders
1998-2004 - NON low drag , normal calipers and strait bore master cylinder.