What kind of car are you getting to replace it? I take it you're gonna take the cash from the Rodeo and buy a used car?
Else wise, I don't really see you getting ahead of the money game if the Rodeo's already paid for. Even though cars do have much better mpg, an average new car is going for nothing less then $17k now, making the payments right around the amount you're using for gas on the Rodeo.
If it's not paid for though, or if you're buying an older used car, I can totally understand one getting rid of something they don't need.
Just be careful buying someone else's "used" car problems.
Have a friend who got rid of his '97 Isuzu Trooper (paid off) for the same reason - gas costs, however, he turned around and bought a brandnew Suzuki car of some-sort.
Granted his gas mileage is in the near 40mpg range, however, his payments are just as much as his previous gas bill on the Trooper, plus his insurance is more due to the newer car.
But I do agree there are a lot of suv & minivan owners who truly don't need them or the room, and what's the point of owning it if you don't need it.
By the way, 160 miles at 1/2 tank is really good for city driving.
Unfortunately, the Rodeo's and Isuzu's in general do not have a high resale value, especially at 160k miles, and if it's a 91-97 it's even lessor of a value due to age. You may not get the $3k, you're wanting.
My KBB value on my '97 with 155k miles, fully loaded, immaculant condition is only worth $1,700 dollars. Selling it personally, I'd probably only get $2-2,200 for it which would be a great loss to me, considering I know I can get at least another good 3-4yrs out of it. I better, I just put roughly $2k in a complete tune-up in everything from O2's to a waterpump.
These Rodeo's get better gas mileage then my Toyota p/up does, but it is 20yrs old.
Good luck to you, there are other Isuzu forums that you can post your for sale information on, two boards in particular are Isuzu fanatics that just may get you a quick sale.
FWIW - if you're not going to keep it, I personally wouldn't do anything more then you have to to sale it, otherwise, it's just that much more money you're going to be out of.
If it's running good, no CEL lights are on, call it good and slap a for sale sign on it.