vibration damper thoughts

[Hop along cassidy]

Does anyone think this could be why i'm getting vibration from my jakes? Over 1500 rpm not much if any vibration but 1400 rpm and below feels like the motors going to come apart. Cummins rebuilt the jakes replaced wiring harness compression test ipt test over head adjustment checked turbo and vgt everything looks good checked with computer on test drive check all settings, even settings on the transmission even hooked up to trans on test drive with computer. Its like the jakes get weak and massive vibration. Help