BUICK ENGINE LOW POWER

My Car Is Losing Power Going Uphill With The Pedal To The Floor And Starts Overheating But Turning On Heater Helps Keep From Getting Too Hot...

It's Been Running Really Dodgy. Would Stall At Stops Intermittently. I Replaced The Post Cat O2 Sensor And The Maf. It Ran Way Better...

When Accelerating Or Under A Small Load Like Going Up A Slight Incline Even, It Completely Loses Power And You Can Hear It 'gasp'...

Put New Battery, No Power Shows At All. No Lights, Sounds, Ect. What Could Be The Issue?