yesterday, my mechanic and i took my truck out for a test drive. the trans works well but there is a vibration that i noticed almost immediately. we got out on the highway and took it up to about 70mph and the vibration was bad and got worse as soon as i put in the clutch. putting the trans in neutral made no difference. the vibration only subsides as the speed decreases. so we're thinking that the driveshaft needs to be balanced. i am going to suggest a test to unhook the driveshaft from the trans, start the truck and run through the gears. no vibration means that it's in the driveshaft, right? could this also be a trans alignment issue? any advice would be greatly appreciated. thanks!