Sounds like you have ruled out most all the external inputs that could trigger this code?
Listen and understand what GDE is trying to tell you, the on board engine management computer (OBC) has a
built in internal atmospheric pressure sensor that measures the barometric pressure of the ambient air and feeds this information into the computer so it will know how to manage your fuel injection rate. This is just one of many inputs the computer uses to determine injection rates based on pressures, temperatures, and others...
Changing or repairing the OBC as GDE suggested may be your only option to correct your problem.

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Supporting Vendor and Moderator of LOST05 Jeep Liberty CRD Limited 
Ironman Springs/Bilstein/Shocks
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Carter Intank-pmp
2mic.Sec.Fuel Filter
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IronrockArms/wwdieselMount98 Dodge Cummins 24 Valve