I am banged up right now.Neck surgery,with full cervical collar.So im fighting every instinct i have to just lay down and look and let the wife put in 'R'....
But the one with all the common sense (wife) but the brakes on that
adventure.

Now this is a 96-95 454 engine Edelbrock Performer 2.0 Barry Grant 750vac sec with electric choke (hooked up correctly which means one pump hit the key fires right up fast idles at 1200-1400 when warm 750ish)Cer coated headers -true duals all one ton gear under it.Both axles were done not long before i bought it.400 turbo_205 tc_custom drive-shafts_

In drive makes no noise when it idles down very little....

Im thinking trans mount broken..??

just guessing at this point

 

sounds reasonable. the only other things that come to mind is u-joints or slop in the rear end.

:chug:

 

I agree with U joints. Easy to check (I know custom driveline ect.) but those may not "clunk" while driving, but will when backing out. Could be a tranny mount, those are easy to check also.
I had rotator cuff surgery in March, my advice is to get yourself healed, don't go crawling under your truck.