my 1998 caravan has been having very odd fuel readings on the gauge. it will go from half tank to empty in about 20 miles then when i put in about 4 gallons of gas itll go back up to half tank. also the computers calculated distance till empty reading goes down very quickly. it has the 3.8L engine. could the sender be going bad?

 

Chryslers fuel sending units are not known for being that great. I'm having a similar problem in my truck.
You can try using some good quality fuel system cleaner (such as Chevron Techron). That might help the problem.
I believe that the fuel sending unit is integrated into the pump (it is on the trucks). For most people, it isn't worth the cost to replace the fuel pump just to get an accurate fuel reading. (i.e. for the cost of a new pump, you can buy a lot of gas!). Simple math will help you to know when your running low ("I get 20MPG, I have a 20 gallon tank, I've went 350 miles, I should probably fill up.")

 

My 2005 GC has been really screwy since we bought it. Its normal 60% of the time then it will never read full, then read empty with 7 gallons still left. I just watch my miles anyways. Sure enough when it went to the dealer they filled it up and it went to full. Oh well, a free tank of gas.

 

If it's driving you crazy you can always remove the pump and sender and inspect the rheostat for foreign material interfering with the contact of the sweep arm.