Do you know if there are any Diagnostic Trouble Codes/check engine light stored in the ecm? I have not personally seen this, but I did some research and have come across a few Cadillacs with same problem, more than likely this is going to be your Evaporative emmissions (EVAP) canister purge solenoid/valve malfunctioning. The EVAP purge solenoid controls the flow of vapors from the EVAP system to the intake manifold. This normally closed solenoid is pulse width modulated (PWM) by the control module to precisely control the flow of fuel vapor to the engine. The solenoid will also be opened during some portions of the EVAP testing, allowing engine vacuum to enter the EVAP system. If yours is staying open while fueling it is letting more than ussaul gas fumes into the intake creating a hard start condition. Hope this helps.