After having guide pins seize on my gasser I would always lube the guide pins with high temp grease every time I worked on the brakes. I then found the grease would cook into a hard varnish, so now I also clean off the old grease first. If you can't move the caliper back and forth by hand on the guide pins, they need to be cleaned and regreased.
If the caliper is loose on the pins, the pins, and possibly the caliper, need to be replaced.
I still had rough movement with new pins once. Some really fine sandpaper polished the guide pin bores and guide pins, and then everything slid smoothly.
Also make sure your brake pads are wearing flat. If you get some slop in your guide pins or wheel bearings the pads can wear at an angle, giving a bit of a door stop effect. Another thing that can cause this is age and the brake bracket bending, so look for that and replace if needed.
I believe in the "disk brake quiet" stuff. Your piston is supposed to retract very slightly via its seals, and the "disk brake quiet" stuff is a glue that will help also pull back the pads.
When putting in new pads I check they move smoothly, so they can move in the bracket as they wear. You might need some fine sandpaper polishing.
Check the handbrake cables move freely, so the handbrake fully releases.
If the brake disk is rough, that is another source of brake drag. Turn or replace.
This one is subtle. I had wheels that were tight for a rocking motion, but would telescope in and out a bit (normal for a solid axle car). When I replaced the axles they were a slightly different length, and the brakes rubbed causing rapid wear. I finally fixed that by putting thin spacers under the brake disks. Moral of the story is make sure your wheels are tight as it can affect brakes.
I have read about folks going for the ultimate efficiency making sure the piston is perfectly round, and the caliper piston bore is round.
I wonder if stainless steel disks have less friction than cheapy iron ones?
