[ben333]

Try shortening front brake lever plunger on master cylinder. You should have 2-5 mm free play at plunger before it touches piston. If you have free play you likely have plugged return port in master cylinder. This can sometimes be corrected by reverse bleeding. Pump brake to move pistons out slightly and manually return pistons into caliper bore simultaneously. The returning fluid sometimes clears blockage. If not the master cylinder would likely need cleaning/rebuild. Not likely caliper is causing your trouble as you claim pistons are movable. No worries about one piston moving before the other. It's normal. Check back as needed if problems persist

I can't believe it, but this actually worked for me! (Pump brake to move pistons out slightly and manually return pistons into caliper bore simultaneously. The returning fluid sometimes clears blockage.) I had just done a caliper rebuild (seized) and was getting drag after install. Never thought this simple process would work, but I tried it right before I was about to rebuild the master (again). Thaks @augiedoggie for this great tip!