A few years ago I bought an '06 Subaru Baja Sport (favorite car I've ever owned!)  The engine was replaced because the seller bought it for his mother and the CHECK ENGINE light was on and he didn't want to give his mom a car that was having a problem so he put a new engine in it.  The car had a few "minor" issues that I had taken care of (the mechanic I use is fair and honest (but DESPISES Subarus--- he's a Jeep man {black}:vomited: )

I live in PA and there are a lot of hills and there is a large one on the highway right by my house that every time I start to go up the hill, it downshifts (which is normal for any car) but when my car downshifts on a hill, it feels like the transmission is going to land on the highway and I swear I've heard the tires "chirp" before when it did it. 

The transmission fluid level is where it should be (according to the stick), I've taken it to my local Subaru dealer and they looked at it and said that it was because my transmission mount was cracked OR because I (previous owner) have an aftermarket filter on it---I had the mount replaced and I REALLY don't think its the aftermarket filter that is causing the problem.  

Do you have ANY suggestions?

Thank you very much..

-Jason