braking problems with GM 4500

I am on my second 4500 conversion which I use to pull a 34' gooseneck horse trailer. When I brake there is a severe "bucking" as if the truck is going into hyper ABS. This is happening with or without the trailer electric pluged in, as to eliminate a malfunction in my trailer brakes. It also happens with the truck attached to other large trailers.
I have heard of three other people having the same problem, but no one can seem to find the cause behind the "bucking" thus be able to fix it.
Is there anyone else out there having this problem?

[KAYE RIVERCITY]

....turn your drums or discs....change shoes or pads.....geofkaye