2011 Honda Civic Coupe - Vibration in seats after changing motor mounts

Hello,

I recently brought my 2011 Honda Civic Coupe (5 speed automatic, 4cyl.) in to have
the motor mounts replaced after hearing a loud rattling noise under the hood in park
and idle before the car was warmed up. Once it was warmed up, the rattling noise went
away.

After I got it back from the mechanic, the rattling was gone but now my seats are
vibrating during idle, park, and reverse. It's even worse when I have the A/C on. Before
I took it to them, the car idled so perfectly that sometimes I'd think it had stalled. I've
taken it back to the shop and they checked it over again but haven't been able to fix
the vibration.

I've also noticed that the RPMs are a lot higher when I take off from a light or need to
accelerate quickly. It never used to go over 3k RPMs unless I floored the gas pedal
(which rarely happened) but now even just accelerating normally onto a freeway makes
it shoot up to 4k RPMs and it will hang anywhere between 3k-4k until I stop
accelerating and it will eventually come back down to normal. If I'm at a stoplight on a
hill, RPMs will go up to at least 3k when I take off from the light. Again, it never did
that before getting the mounts replaced.

What else could my mechanic be missing? I'm at my wits end with this car and could
really use some help.

Thank you!