The Mopar MaxCare extended warranty periods are based on 1st sale in service date and miles. So all of the various year/mileage terms end at the number of years and miles counting from 0, not from when you bought the warranty. I.E. if you buy an 8 year/100,000 mile contract the day you buy the car it lasts for the full 8 years and 100,000 miles, if you buy that same warranty just before you hit 3 years and 36,000 miles (the end of your factory warranty) it will only last for 5 more years and 64,000 miles but it will cost more than it did when your truck was under 12k or 24k miles not counting any price increases during that time you waited. The only reason I'd wait is if you aren't sure you are going to keep it but even then you would be able to get a pro-rated refund on the remaining warranty.