How much will such a swap, or any swap for that matter, cost you? Even a basic swap only ahs a chance of justification if the existing motor is shot.

If you drive an average of 10,000 miles per year, the difference between 15MPG and 20MPG at $3/gal will save you $500/year. That will take you three years to recoup even a modest swap at $1500 in cost.

Sure you can do for less, if you get lucky on donor parts, etc. you could also spent plenty more.

Do the swap because you want to, not because you don't like the MPG. Like we always say, you're driving heavy metal with a fully boxed frame and the aerodynamics of cargo trailer.

[Note: None of the above applies to going diesel...]