Most likely,your loss of power is caused by something other than a restricted exhaust. Put your hand near the tailpipe while it is running and see if it has a pretty firm force on your hand. (Obviously, you know it will get hot quickly,so be careful). I would recommend checking spark plugs/wires to begin with,although there are numerous possibilities of cause of power loss. Good luck and God bless!!
A partially plugged catalytic converter is more probably the cause of a restricted exhaust. Run the car at night to see if the cat gets red hot. A plugged cat is a symptom of a more serious problem. If the motor has been running too rich the cat will be destroyed.