I have a GMC Sierra 5.3l vortec automatic 4 speed overdrive 2003 short wheelbase pickup. I put a dubble locker editon possie rear end in with4.10 ring gear & pinion in. I had a stock rearend and 3.42 gears. Now when I get to 110mph or a 120mph (off road) I have vibrations in the floor. I feels like it is in the drive shaft or trans. Could anyone andvise what this problem could be? Before when stock I did not have this trouble what is wrong? The gears where set up right and all new seals put back in. PLEASE ADVISE IF YOU CAN HELP ME!