2005 Ford Escape running rich - 3.0?

[Kevin]

Bought fixer upper, would only idle, changed all plugs and rear coil packs, plenum gaskets. Checked compression, ok. Found rear converter clogged. replaced. Runs now, code P0420, catalyst problem. Replaced both lower O2 sensors. slight miss at idle, worse above 50mph, runs rich, can smell gas, occasional backfire into intake can be heard. Can't get upper O2 sensor out, improper tools. Takes about 40 miles to set "Check eng. lite". Suggestions