The engine starts to shudder and lose power, I let up on the gas pedal, and there's a strong odor of gas.
loss of power and gas odor on 1993 Chevrolet Lumina
You did not supply very much information. The strong odor of gas would suggest the engine is getting to much fuel. There are a lot of different faults which could cause the engine to get to much fuel. The first place to start would be to check and diagnose any fault codes stored in the engine control module.
More on the problem - when on the highway the car starts to shudder and lose power. I let up on the gas pedal and smell the gas. When I push back down on the gas pedal sometimes it does nothing but make the gas smell strongerd and sometimes it accelerates as it should and the gas odor goes away. When the car stops, it dies. When trying to restart, again there is a strong odor of gas, but won't start until the gas pedal is floored. Then there is a large cloud of white smoke from the tail pipe, and the motor idles rougher than normal for a few seconds.