[PK55Z85]

"sensitivity"....this isn't Cosmo dude
just teasing...there is no adjustment for the abs
it's either working or not...now you might have a wheel speed sensor reading erratic or a wiring harness with some kind of open or short giving the control module erratic signals
it also sounds like it could be a normal condition...depending on your driving habits. it's not abnormal for this type of condition to happen while stopping over bumps at a quick rate of decell.
if a wheel momentarily loses traction. but you should NEVER take foot pressure from the brake pedal...in doing that your telling the computor there is no more need to slow down...thats not the trucks fault.