1993 Chevy Van brakes not releasing

The front brakes take 2-3 minutes to release after taking your foot off the pedal. I have replaced the calipers, the master cylinder, and I have completely bled brake system with new fluid. The van has set up a lot over the years, and it has 4 wheel ABS. I don't know if it's ABS system, the proportioning valve, or whether it needs a complete system flush or what. There are no warning lights on. I am currently on unemployment and don't want to put it in the shop unless I have to.