2001 Ranger drinks a lot of gas

It's a 4.0L 4WD automatic.
It's got approx 155K.
It was getting lousy mileage, maybe 10-12.
I took it in to a private shop who has always been honest and, he did OS's, EGR, plugs, etc.
That was 6 months ago.
It gets about 8-10mpg.

BTW-I only use the 4WD at the boat landing or when I'm in deep snow.
It is now May and, it's in 2WD.

Is the 4.0L a lost cause for mileage?
This is my service vehicle and, it's eating up a lot of my income.

Would it be worth it to take it to a Ford dealer and have them analyze it?

Any suggestions would be appreciated.

It should be getting much better mileage than that, It would pay you back in gas savings eventually to get the problem diagnosed and fixed