As far as your lack of power, it sounds like either a plugged up catalytic converter, or the fuel pump is failing. To determine if the exhaust is plugged, you could remove the oxygen sensor from the exhaust and drive it under load to see if some power is restored. It will of course be much louder. You could also install a pressure gauge to measure the amount of back pressure.
To test fuel pump, connect a fuel pressure gauge to the Schrader valve and drive it under load. Fuel pressure should be above 35 psi and not drop below 30 psi under load. If you haven't already, make sure to check your air and fuel filters first.
