I think that is one I would definitely run by the dealer and double check. Just to be sure it was, in fact, done.
Try this throw a set of XIED's in the thing ride it if it don't run better return them Your problem dose not sound like tranmission or rear end problems
But I have notice that EG runs smoother and quieter when it's cooler outside. On hot days it runs about the same until the engine warms up, then it’s nosier and not so smooth. Maybe the XIEDs will help.
Thanks
What oil are you using?