RE: Sounds like the G28 sensor. It costs ~$150 and is a 10 min job. .
 

The colant temp sensor that would cause stating problems is behind the motor, its a direct imput to both the ECM and Instrument cluster. The one on the radiator is just a dummy sensor, and so is the other one on the heater core. (emergency sensors) that provide back up input to the ECM in case of failure of the main CTS sensor.
Your still looking at a crank sensor IMO.

RE: Sounds like the G28 sensor. It costs ~$150 and is a 10 min job. .
 

Thanks Auditech. If that's the case, then I wouldn't imagine that the coolant temp sensor that's causing the problem would have been affected by the radiator service... any way of knowing which crank sensor or should I just replace both? Anywhere I can get my hands on them sans-dealer?

RE: Sounds like the G28 sensor. It costs ~$150 and is a 10 min job. .
 

You might wanna try www.ecstuning.com for the sensors, the dealer can look it up on ETKA parts info for which sensor but im not 100% sure on that.