Brake issue

[Android04]

So I just picked up a 1994 Silverado 2wd single cab. It was bought as a project and once we got it unloaded we noticed some funky stuff with the brakes.

Here is what’s going on. Brakes are a little spongy but work fine and I can figure that out but the part that has me looking for help is the pulsating it’s doing when completely stopped. This is not a rotor issue as it happens when sitting completely still at a red light, stop sign, etc.

If I try and brake torque the truck it will kick the brake pedal back so hard it nearly kicks my foot off. The truck idles fine and runs great.

So could this be dirty/bad ABS sensors? I don’t get an ABS light or anything that I’ve noticed. Any thoughts?