So I just recently did the 63" spring swap on my 1987 runner and everything flexes beautifully and rides as should be expected, however, I am experiencing a slight vibration when down shifting. I've been under there countless times make sure everything is tight. lined up properly, measured correctly etc. The only thing I can think of is I have the interior pretty much gutted and there's not that much weight (not that interior adds that much weight anyway) and could be the tires chattering. Any ideas? Your guys' advice is always appreciated. Thanks!

 

What are the driveline to diff angles, During downshift the diff pulls downward and could be binding the Ujoints.
Last I read 3 deg optimal, 7 deg max and should be same on both ends unless you have a dbl cardan on one end.