Just as in everything in life, there is the good, the bad, and the worthless. On used 4x4 trucks, I usually recommend an extended warranty if of course you get the right one. We've all got friends who bought extended warranties and when they tried to use it, it was worthless. The biggest reason I've seen was clutches. Even the new factory warranty doesn't cover clutch discs, belts, hoses, and brake shoes.

With the equalization of the Internet in bringing vehicle prices out in the open, one of the last havens for auto dealerships to make money is extended warranties. But there're not all bad. Don't get talked into them until you can do your research. I know the friendly finance manager wants you to buy it now, telling you how easy it is to add it to the auto financing. If it's a new vehicle, you have until right before the factory vehicle warranty expires to buy an extended warranty and get the best coverage and price.
And most warranty companies will finance you if you need it latter on.

Don't get worried about missing an opportunity to get a good deal on a warranty. Your credit union, insurance company, or the Internet can help you find a good warranty. Some companies will let you try out the warranty first.  A high percentage of the time you will never need the extended warranty, just like life insurance and crop insurance. And on cars you use it even less. 4x4 s have twice as many of the expensive parts which is why I recommend it on a used 4x4. Just one major repair will cost as much as the warranty. You won't always know how the truck was used before you. It might have been raced to the airport often, or used to chase coyotes or it might not have even been serviced once. I know people who trade cars every couple of years, and never change oil, filters or anything else. You have to decide your own risk tolerance. But always ask a lot of questions and make sure you get answers before you sign.