One problem related to power assist brake vacuum has been reported for the 2001 GMC Jimmy. The most recently reported issues are listed below.
Vehicle has non-engaging transmission as at times it will not shift though it is an automatic and sometimes it starts out in 2nd and then drops down to 1st. Service engine soon light illuminated on 3 occasions as there were emissions problems. Front end makes constant popping noise. Problem has been lubed on 3 or more occasions as well as coil springs have been replaced and lubed. Brakes went completely out while trying to stop at an intersection. There was a rupture in the brake booster.