Congrats for finally hitting the road! Seems like getting up to 50mph in an ol 1 ton means you got a lot of things right.

u joint angles?

Sounds like it's worth it to do more test driving and replicate the noise under more specific conditions.
A hand at the base of the shifter might help to feel if/when/how the driveline is shaking.

PS. I'm not a sm420 expert yet, but mine seems in really good shape despite having gear noise sometimes

Last edited by Ott3r; 10/24/2019 12:16 AM.

'59 Chevy Suburban, NAPCO