97 K2500 Suburban shaking when braking(not rotors)

[j cAT]

well not sure what your bitchin about... vibs when the brake pedal is down correct ? well if its parked out side and sits for months a rust will cause an issue.
drive it for 20 miles a week and the problem will go away .. new rotors/drums will rust when sitting in your climate.. now if your in tucson AZ not a problem with rust LOL....

If you now have a 2015 GM truck ??? keep the old GM truck probably gonna need a new engine on the new.use the old as a backup ..

remove the drums have them checked for china sloppy machine work...could also be rear axle seal oil leak.

don't know any info about the work/insp your doing now on it.