From a $$ standpoint, the clear winner is new fuel tank for the Frontier, but as you pointed out it will add weight. You're close enough to the limits of the truck now that I'm betting that you won't like how it handles with the bigger tank full of fuel, and will look to upgrade after spending $2300 on the new tank. Been there, done that with trucks and trailers.
Find something pre-owned and you split the difference between the cost of the new tank and the cost of a brand new truck.
One of the reasons I went with a Ram is because they have an easy VIN look up tool that will show you the window sticker of any truck from the last 6 or 7 model years. I found this to be really useful when you're shopping for a pre-owned truck and need info on not-so-obvious stuff like rear axle ratio, optional tank size, and the like.
Here's the
window sticker on my 2015 Ram, just replace the VIN at the end of the URL string with whatever truck you're looking at and it will pull the sticker.
I had a nationwide search running on TrueCar, Cars.com, and AutoTrader for about 6 weeks until I found this truck. I wanted a one-owner, clean CarFax Ram being sold by a Ram dealer. No used car lots. I looked a LOT of VINs, but if you are willing to invest the time, you will find what you're looking for.
