Thats not alot of milage on the brakes for this truck, but its no longer under warranty. This is not real common on the yukon and this is not normal. You have a rotor or rotors that are warped/out of round. It may pulstae a little bit during normal braking but get worse when going down hill. This is due to the brakes getting hot, the puslation will get worse.
GM has a bulletin for a concern that may be the issue that caused this.
#PIT4611: Front Brake Pad Spring Clip Design Change - keywords appearance drag heat hot noise pedal premature pulsation repeat rotor scoring vibration wear - (Mar 26, 2008)
|Subject:||Front Brake Pad Spring Clip Design Change|
|Models:||2007-2008 Cadillac Escalade, Escalade ESV, Escalade EXT|
| ||2007-2008 Chevrolet Avalanche, Silverado, Suburban, Tahoe|
| ||2005-2007 Chevrolet Silverado Classic with RPO JF3 or JF7|
| ||2007-2008 GMC Sierra, Yukon, Yukon Denali, Yukon XL, Yukon Denali XL|
| ||2005-2007 GMC Sierra Classic with RPO JF3 or JF7|
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
During mid production of the 2008 model year a design change was made to the front brake pads, pad spring clips, and caliper brackets. This new spring clip is designed to pull the pad off the rotor slightly more than the original design. This helps to reduce front brake noise, rotor pulsation, and helps to prevent metal transfer between the pad and rotor (scoring). The pictures below show the differences between the 2nd and 1st designs. When servicing a 2008 model, ensure the correct parts are used. It is not recommended to install the new/updated parts on a vehicle built with the original design parts due to future servicability concerns.
You may want to take the bulletin number which is pit4611 and have them inspect the brakes for this issue. The only way to get rid of the pulstaion is to machine the rotors.