My .02 cents worth.....
My service van is a de-rated 17,000 GVW truck, with a 5L engine*, I drive 16% grade roads here at 11,000' above sea level, I keep up with all traffic , but have a little trouble with on ramps in rush hour driving, not to bad, I can live with it. On a 'baby-da-h311' out of it test, I can pull 14MPG on a flat drive at 5280' MSl @ 55 MPH (I will admit that the conditions need to be near perfect, I settle for 10MPG the rest of the week)
Every engine needs to develop good vacuum down the road, and get to speed with out dumping in a lot of extra fuel or dumping it in to course.
Before I touched the program, exhaust or intake manifold , I would get the 'cam-card' specs or degree the cam. and go from there.
Degreeing the cam is over some peoples heads, granted, but getting a vacuum reading down the road is perhaps a good place to start. Installing a vacuum gauge to the interment cluster , along with if you like them an air : fuel ratio gauge that drives off of the O2 sensor(s) cant also Tailor your driving.
Comp Cams , is about my first place 'cam shop' anymore, there are a lot of other companies, but Comp has a lot of grinds for a lot more engines in most cases.
From the hip, I would be looking at an 'Extreme Energy' or 'RV" grind , A better then stock cam** in most cases will correct for any gearing or engine : wight problems that cost you money at the pump. At near $3.00 dollor a gallon gas, it don't take long to pay for a cam.
I would not blink thinking about swapping the cam out of most stock engines. You will gain TQ and mileage, period.
* I did a lot of work to the 5L engine and transmission to make the power I needed.
** The biggest most often mistake is going to far with a cam grind, just a couple 'grinds' from stock can make a world of differance, going 1 grind to far can make a world of hurt to some engines/drives.