Trailer brake and ABS

[Starlight]

Im shooting from the hip here but i would closely inspect cam bushings for being dry on the axles that dont apply the brakes as fast. What might be happening is your front axle that applies quickly might have cams that move freely where as the rear might be tight and cause a delay. The hendrickson intraxx system is bad for that. The inside bushing will lubricate well because it can purge easily when greasing but the outside gets less grease. I believe the outer cam seal is tighter than normal on the intraxx system and causes it to only partially grease. My bro's flat deck has this going on right now. The inside bushing is nice and tight but the outside is so worn out its caused the lower brake shoe to be slightly more worn than the upper. Just something to maybe look at.