It sounds like you have an electrical problem not a key problem. As more systems power up following the start sequence, and you have a questionable battery (the electrical resevoir), the voltage will start to drop as the loads increase. Once the voltage drops below a certain value, solenoids will start to de-energize, electronics will start to shut down...the engine will shutdown.
General automotive troubleshooting values for electrical systems are:
1) 12.0 to 12.5 VDC with the engine secured.
2) The voltage should not drop below 10.0 VDC during the crank sequence.
3) With the engine running, and the battery near a normal charge, you should see 13.7 to 14.2 VDC.
Post cleanliness (O.D. of post to I.D. of clamp), as little as 0.5 OHMs can cause an IR drop significant enough to cause electrical problems.
Most complex problems are rooted in the fundamentals. Don't find a NASA grade solution to a Home Depot sized problem.
I don't know if the engine controls on the 2003 are ETS (energized to shutdown) or ETR (energized to run), but if the system is an ETR low battery voltages "will" cause a shutdown.
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