Does it totally disappear in 2nd gear?
They do have a very mechanical tingle to them in 1st/2nd, but to have this excessive vibration in just 1st seems odd.
I think since 1st gear transmits the most torque, which is the main thing, and it is also going the slowest it will too, so lower frequency vibrations present... maybe a loose rear gearbox damper? Worn engine mounts as Tref mentioned?
Just weird how it's started after repairs?!
Dave