Hello and thank you for contacting us. This is Dwayne B. and I’m an expert here and looking forward to helping you today.
The only way you may have a right to return the truck is if there is something wrong with it and they refuse to fix it or are unable to fix it in four tries.
Many people are under the impression that they have a right to cancel any contract within a certain number of days but that's just incorrect. The "urban myth" started because you do have 72 hours to cancel certain deals that are done at places other than the seller's place of business (ex. a door to door salesman). Most courts have stretched this to allow for you to rescind a contract for a vehicle if you bought it at a place other than the dealership, such as a car show, a mall, etc.
If you believe that there is a defect in your vehicle as opposed to diesels just being "smellier" than gas vehicles or you just not tolerating diesel fumes as well then you would need to hire a lawyer immediately and have them start documenting your attempts to get the vehicle repaired.
You can find a lawyer to assist you by going to www.lawyers.com and in the section for Area of Practice enter Civil Litigation or Consumer Law. Either of those will have the skill set you need.
If your question has been answered then I'd offer my best wishes to you and ask that you please not forget to leave a Positive Rating so I receive credit for my work.
Of course, please feel free to ask any follow up questions in this thread. I want to be sure that all of your questions are answered.