Driveline Grind/Vibration

[BiltByMe]

We installed a 4 inch skyjacker suspension lift on my 1970 GMC K2500 a couple months ago and realized that the shims under the rear axle were not quite right so I switched them around to get a better pinion to output shaft angle. (closer to parallel). After doing so I now get a bad grinding and vibration that sounds like it's coming from the transmission when i let off the throttle at about 45 mph. Originally, I was thinking that with the lift the stock driveshaft was now too short and pulling on the output shaft yolk. We got measurements with the suspension at full droop and at compressed length. Contrary to my belief the driveshaft got shorter at full droop than at loaded length. So now i believe that the stock driveshaft is too LONG for my lift and its bottoming out the slip yolk of driveshaft and shoving in on the output shaft potentially munching the bearing. Has anyone else had a problem like this or know how to better diagnose what I have going on?

[geezer#99]

Is it a one or two piece driveshaft?

[HO455]

I think this will get more traction if you repost it in the 4x4 and off road section. And a picture is worth at least a thousand words. Unless you want to post a 10000 word essay on the subject I think some photos will help folks get to the bottom of your issue.