A bad upstream O2 sensor will cause the lean code and abrupt loss of mpg. The upstream O2 sensor is responsible for telling the engine computer how to set the air-fuel mixture. Your O2 sensor is erroneously telling the computer the fuel ratio is too lean which keeps richening the mixture more and more trying to correct it until it is full-rich. That wrecks the power and the fuel economy.
Replace that upstream O2 sensor ONLY with a NTK or NGK O2 sensor, make sure not to install a Bosch O2 sensor which is well known not to work well in our Jeeps.
Can't say what's causing the power steering code, have you checked the power steering fluid level? If it's low, add power steering fluid if your Jeep is a 2002 or older. If it's a 2003 or newer, it requires ATF. ATF+4 would be fine.
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