Gas mileage 05 Ford escape

I have a 05 Ford escape, with 80,000 kms
on it oil changed ever 5,000kms. Recently
just had a new muffler Installed along with
a new cat because the muffler was falling
off. Thought it would fix the problem of my
gas pissing out but didn't happen. I
estimate I get out 15 mpg. Blow threw a
quarter tank of gas in 1-2 hours of driving,
which is a big difference from when I
originally purchased the vehicle. I was
getting a week and a half on a full tank of
gas. I'm going to take it in to a more
respected mechanic shop and see if they
know how to fix it. A guy a canadian tire
said my cat could be plugged. Not a car
guy so any suggestions you guys have
would really help thank!