1999 Other Saturn Models Surging engine, etc.

My 1999 Saturn SW2 is having a issues involving the engine and related parts! A couple months ago the coolant temperature light started flashing and I was told by the dealership that I needed to replace the Engine Coolant Temp Sensor. I did this. A couple weeks later the coolant light started flashing again with the service engine light came on as well. Soon after, the engine started to surge. About two days later, I filled the tank with gas and the car would barely start with the engine surging to 2500-3000 RPMs. A few miles down the road the radiator burst. The following has been performed on the car: New radiator, new ECT, new spark plugs, air filter change, coolant flush, transmission flush, and water pump replaced. The car generally seems to run fine for three-five day intervals, then the check engine light will come on, the engine will surge drammatically, and once the car is turned off it will not restart without a "jump". Now it just sounds awful and not really available to drive. Usually, it appears anyway, that the car starts acting up soon after I get gas--this could be my imagination. Help! I love my car, but I don't know what to do! Thanks!