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This car is OBD compatible most parts stores like Auto Zone can do free code reads. If you can get me the code number I can better advise you. The VSC and trac light come on by default when the check engine light comes on. It sounds like there may be an issue with the drive by wire throttle body system but if you can get a code number I can better assist you.
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You or the truck are not in the country? If I had to make a wager not knowing the code based on the info of the truck driving in limp in mode it sounds like something in the throttle control I have seen problems with them. Try and get the codes and if you need a second opinion on what the dealer is telling you reply to this post. How many miles do you have on the truck?
Electrical warranty is 3 years and 36,000 miles so she may still be under warranty. Have her go to an auto zone or similar parts store (if it is a safe area) and have them pull the codes and get them to me. Tell her not to spend any money on repairs until you get me the codes to verify.