Vibration in overdrive

I mean putting the vacuum lines back to the way the came with the car factory. Whoever had it before me plugged and re routed some vacuum lines. I did not have the vibration before the vacuum lines were all replaced. The vibration did not start until about 125 miles after the vacuum lines were replaced.

Are there any vacuum lines going to the transmission? If there is, pull the line and block it off and see if the vibration stops. I am making the assumption this is an automatic transmission? Go to a trusted transmission repair shop, like AAmco for advice. Even stop in to a Chevy dealer and talk to one of the service reps. If this is a common thing, they should have handled it before. Where is the vibration coming from? The drive-line, front end, wheels, steering, or can you tell if it is indeed the transmission and not the motor at a set RPM?

I forgot, did you recheck your vacuum hoses for proper placement, and any leaks or cracked hose attachments? The hose attachments are cheaply made, and because brittle due to heat and weather conditions, A slight crack will cause some issues. If any attachments had been replaced, are they the correct size for the hoses? I have a 69 Vette that has miles of vacuum lines, and it's sometimes a @#%$#@@& to find a leak.