Shuddering at 20mph

Hello this is my 1st time posting on any type of forum.I have a 2008 Titan SE king cab 4wd long bed 173000 miles. Recently it started to shutter when braking only at 20mph. At the recommendation of Bridgestone I replaced the front rotors and pads. The issue has not been fixed. Two things happened within two days after a long trip the shutter began and the next day the shift cable broke at the column which has been replaced. There is no shaking at the steering wheel I can feel throughout the whole truck. Feels like rear to me. Bridgestone said the u joints feel ok the only issue they saw was the center bearing may be a little loose. Any help would be awesome