This has been a great truck now for 12 years. Never a big repair beyond brakes,battery,etc. Great CD, Great A/C, Great in snow and even trails. Only two complaints; It's a longbed and hard to park at the Mall. It's also very poor on gas- about 12 mpg in town and 18 on the highway.
You won't get 50 mpg with this truck. It is, after all, a truck. I got 14-15 mpg combined gas mile p/gallon with a fully loaded bed (1000 lbs.)!!! (a homemade camper lives on the bed). Otherwise, about 18-20 mpg. I bought this truck used about 4 years ago. It is 12-years-old now. I put in a new battery, and a set of great tires. I do the scheduled maintenance. That's it! It always starts, always runs. No issues. Reliable. Solid.
My grandfather bought this truck new from the dealership in 2004. The whole time he owned it through my childhood and teen years it was phenomenal, and still is today. Recently due to medical issues he had to give up driving and the truck went to me. It is still the the magnificent truck it was the day he brought it home. My wife and I own a small hobby farm and we use it frequently for hauling feed, supplies, produce, animals, and just about anything else you can think of. It's easy to maintain, very simplistic in that there is not a lot of electronics to fail and the gas mileage is unbelievable. We recently took a trip from our home in Western Maryland to the Adirondack Mountains in upstate NY and the truck averaged 34mpg for the trip, and that was with the bed loaded with camping gear. When my grandfather bought this truck he traded in a 1984 Nissan truck for it which had 483,000 miles on it an I expect that and so much more out of this beautiful piece of machinery. If you have the opportunity to purchase a 1st gen (1998-2004) Nissan Frontier with the bulletproof 2.4L KA24DE engine get it. It will be the best investment you'll ever make.