Cost of ownership, 4 cylinder vs 6 4wd

Thinking about upgrading my 2007 4 cylinder manual to a 2006-08 6 cylinder 4wd manual. Truck I end up with will probably have around 100k miles.

Mpg seems like the biggest cost. my current truck gets only about 19. I drive in town mostly and I am fairly hard on it and Go 70+ on the freeway. V6 mpg on here seen to vary a lot. People claiming low 20 while others say 14. What should I expect?

Any other costs I should be thinking of?

Thanks