I'll have a go at this. You say your fuel gauge doesn't work, and that you've been told you have a bad sending unit. Next you're talking about replacing the fuel pump to cure the problem.

You're dealing with two entirely different areas here. The fuel pump has nothing to do with the fuel gauge. You've said that your Trooper runs well, that you just don't have more than a vague idea/guess at how much fuel it has. If it runs well driving down the road, then the fuel pump is okay. If the fuel gauge, the one there on the dashboard, doesn't work,it could be one of several things. The sending unit might very well be bad, the wiring could be bad, a fuse might be bad, a relay might be bad.

Always start with the easy stuff. Check your fuses. Be sure they're good. Check the relay. Change it with a similar relay there under the hood. Check the wiring, run a continuity test if you're able. Finally, look at the sending unit. It has to be inside the fuel tank. You might have to drop the tank to get it. If you drop the tank, wait til it's empty.

Of course, you might have a dead gauge. All these things need to be tested.