Error Code P0235 on 2004 Grand Cherokee 2.7 Lerado

Question

Intermittent: Sometimes engine light comes on when I start the vehicle other times not. Sometimes no power when I pull away other times it is fine, sometimes lose power while driving then stop and pull away it is fine, sometimes lose power then switch off and on it is fine. Sometimes gears wont change then switch off and on and gears are fine (this usually happens if I pull away and not let vehicle warm up, not often). Loss of power and engine light is concerning. Also having problems with battery been drained overnight.