I currently have a '95 F-150 to pull my 2 horse trailer.   I really need to upgrade to something more powerful.  My problem is, I don't understand how to figure towing capacity.

It seems like the newer trucks mostly have 5.4L engines-even the 3/4 tons.  I'm not sure what is important when figuring out the towing capacity of a truck-is it the weight (1/2, 3/4, or 1 ton), the liter of the engine, the number of cylindars. . .???  Also, I'm at a loss when it comes to diesel vs gas engines.  I know both have their benefits and drawbacks, but are there any situations where someone should choose one over the other?

I plan on beginning my hunt to purchase a vehicle this spring/summer, and I'd like to be well educated on the topic.  I won't be buying new, I will be buying a used truck.  Any suggestions on years or models to avoid would be greatly appreciated!

if youre going to stay with ford this site is very useful.

https://www.fleet.ford.com/showroom/rv_trailer_towing/default.asp

are you staying with the 2h?  if so any new model 1/2 ton with a v8 will be a huge improvement over what you have now.  the automotive world has come a long way in the past 10 years.

The easiest and best way to figure the towing capacity of a vehicle is to compare the GCWR (gross combined weight rating)  The higher GCWR  in a model line means  the vehicle can accelerate, brake and steer the heavier trailer.  The effects of axle ratio, engine power, brakes, transmission etc, are all figured for you.

Choose diesel if you want what's popular.  The only  situations where diesel is clearly superior is  high mileage in a short time and high altitudes.  The turbocharger equiped engines are absolutely needed at high altitudes to make up for the rarified air.  If you tow less than say 3,000 miles per year get a gasoline engine.