2006 Subaru Outback/Legacy Wagon losing power

My 2006 2.5l wagon has 142,000 miles, has
had regular maintenance done by the dealer,
and generally has run amazingly well ever
since I purchased it used at 70,000. Recently,
however, my sister back it into a snowball
and broke the connection between the
muffler and the exhaust pipe. This will be an
easy fix that I’m not worried about. However,
in the past I have had some small problems
with losing power at high speeds. If i was
rolling at about 70 mph and tried to
accelerate, I would lose some power. I’d still
accelerate, but it would be splitters and
jumpy and the tachometer would twitch as it
slowly accelerated. This happened only
slightly, then went away.

Now, however, the same thing is happening
when I turn the car on and at low speeds.
When I go from a stand still and try to
accelerate, the vehicle acts as if I’m out of
gas and the engine is spluttering as it
misfires. I was curious A) if the muffler
problem could be messing with compression
or just generally causing a problem that
results in this loss of power and B) any other
explanation for the loss of power and
spluttery acceleration.

Any help would be greatly appreciated!
Thanks so much :)