2003 Infiniti G35 fine vibration starting at 40 mph

We had to have the seals replaced in between the engine and the
transmission. They had to drop the transmission and ever since we have had  
a very fine vibration that starts at 40 mph. We had a bent rim we didn't know
about so we replaced that. We have new tires. We don't notice it on really
bumpy roads or roads that aren't really smooth. Normally we would treat it as
a don't worry about it until it breaks kind of thing, but we are about to take it
on a four day drive out of central Mexico back to our home in Florida. Don't
really wanna be on the side of the road. Any thoughts?