Maxima 2000: can new muffler cut MPG by 3-4??

A couple months ago, my 2000 Maxima with 68,000 miles start making
terrible clunking noises from the muffler area.

My head wasn't on straight that day and I took it over to Meineke.  A pipe
was rusted out and hanging...they said even though the original stainless
steel muffler was fine, they had to replace the muffler to replace the
connecting pipe.  I said "fine".

I know...dumb move in hindsight and I wish I would have taken it
elsewhere.

Well the Meineke muffler was $220 or something like that and looks/works
fine.

However I swear I get 3-4 MPG less than I used to.  Possible?  I also got
the MAF sensor replaced in the same time period...