which is best truck for 5000Lb trailer

The new diesels are not a good economical choice. The manufactures have crippled the fuel mileage on them and not even with a $1,500.00 programmer are you going to get really better fuel mileage. The 1/2 ton trucks are more than enough truck to pull a 5,000lb trailer. If you are not going to tow more than that you will be good. I would go with a gear ratio somewhere around the 373 mark. With most transmissions being 6 speeds or more now you will usually have a pretty high gear for when your not towing. I pull my 8.5' X 24' trailer, with a GVWR of 10,000lbs, with a Toyota Tundra and it pulls the trailer almost as good as my 3500 Dodge 6.7l in stock form but I have the diesel because I need it to pull my much larger trailer that the Toyota can't tow. I personally think that the 3/4 ton trucks are a better buy for your money because you get a whole lot more truck for about the same price as a 1/2 ton but you will sacrifice some fuel mileage and the ride will not be as soft but the 1/2 will do and I wouldn't go buy something else if I already had a 1/2 ton. It pretty much comes down to how much you are going to tow because 3/4 ton truck will hold up longer if you are towing a lot.