I had a slight vibration on my 81 Caddy,which drove me crazy.
I had just replaced EVERYTHING in the front suspension & steering,4 new tires,balanced(they had to rebalance to get it right)
Rims & hubs where straight,CV joints were nice-no play
Drove me crazy !
At first it seemed random,would come & go while cruising on the highway
After carefully monitoring,I noticed it would only happen going UP hill - Not on level ground,not down hill.
Straight road or curved road didn't effect it- Only Up hill
I finally got fed up and threw a pair of New drive axels in ( everything else was new,so why not ? )
Solved the problem - No more vibration
Sometimes narrowing down the source of vibration-is a time consuming pain in the A___ !
Best of luck - Hope yours is something simple
Mike