The best dually diesel pickup truck would be Chevy or GMC 3500 with Duramax and Allison transmission.
Dodge. Straight up.
The best mileage for a three quater ton diesel pickup truck is 15 mph. It will only change if you going on a stopping trip and you don't use a highway on a long trip.
Considering that a diesel pickup truck can't use gas I would say that there aren't any diesel trucks that get good gas mileage. If you were wondering which diesel truck gets the highest miles per gallon then I would say you should look at the Dodge Cummins diesel.
The best things about a diesel pickup truck are that you will not have to fill up the tank as ofter if you are driving a lot. Another advantage is that they have glow plugs and if you ever have a problem with starting you know where to check first.
Diesel engines were not a factory option until the late 70s, so if you find a 60s pickup with a diesel, it has been switched after it left the factory. Installing a diesel engine in a 60s model Ford pickup would not be the easiest conversion, but it could be done. Motor mounts would probably have to be fabricated, and you would probably have to change out the transmission, also. Best to find an engine/transmission combination that has already been proven to work together. The other consideration is finding a diesel engine with the horsepower and torque necessary for the truck.
If you want gas mileage with power, and reliability, particularly with the transmission, Cheverlet is hard to beat.
2006 and up . Gm 3500 hd 4x4 z71 with the duramax diesel and Allison transmission.
According to many the Ford F-150 is the best selling pickup truck in the US. Ford.com has more info on this vehicle.
2 tons
The right type of fluid will keep a car running at its best. The 1995 5-speed Nissan pickup uses 75W-90 Gear oil.
I depends on how much your towing and is the vehicle new or used. The best are full framed... I.E. pickup trucks. Under 2,500lbs. a compact truck Nissan frontier is currently the cheapest with a base of $18,000. $3,000+lbs. I would only use a 1/2 pickup or larger suv. Compact trucks/Suvs might be rated up to 5,000lbs. but they aren't built with the durability, transmission/brakes, frame strength that 1/2ton+ pickups are designed for. The Ram eco diesel is the best for towing a car, ram has the lowest base price of the half tons and the only diesel for 25+mpg. The diesel is better compared to the same truck with the larger gas engine.