1991 Dodge Shadow Recently Bought 91 Which Drove Well Until Would Lose Power

I recently bought a 91 dodge shadow which drove well up until recently when it would lose power at higher rpms. I changed speed sensor and the belts it drove fine. Started happening again this time more often and the rpms varied. It was usually colder and there was moisture in the air. The ignition switch was changed before i bought it and seems to be put in wrong could this affect the car losing power or not starting? The car wouldnt start this morning and no power either.