new engine chevy 350 th350 trans new flax plate torque converter and rebuilt trans 1 yr old its on a 77 chevy k10 been driving it fine for months engine replaced 8 months ago. just recently been getting a vibration between high 1st gear and low 2nd gear 18-2100 rpms after getting speed it goes away pretty much everythig has been replaced body engine trans mounts ujoints tierods balljoints. the vibration is very minimul but makes me paranoid as i dont want it to hurt anything.has ahughes 2000 torque converter fluid levels are good it drives just fine but that vibration is concerning

 

Tires, driveline imbalanced. But ...
This is a thirdgen forum , maybe you should join a truck forum.

 

need to figure out if it is engine rpm related or trans output speed related, or final driveline speed related...this will help you to start narrowing down your search for what to look at.