The gas guage still reads full when there is only a half tank

THIS MEAN YOU NEED TO CHECK THE LEVEL SENSOR INSIDE THE GAS TANK MAYBE GIVES WRONG READING

check the sending wire to see if you have a bare spot
if you don't know where the sending wire is we don't know either
as what year
model
etc

from what you are describing you have two(2) different problems
1- the wacky gauge- its acting like a grounding issue- wires are crushed/smashed on tank connector
2- not filling - venting issue- vent line to top of tank pinched
3 solution- run tank down to 1/4 or less and DROP tank down to inspect wires and hoses- sounds like at some point in time the tank took a hit and wedged itself upwards against the underside,pinched the vent line so there is too much pressure in tank and also crushing the wires/plug causing the erratic readings(worse with less weight as the tank moves more)
if unsure of how to do this- you can get a manual such as a HAYES book at auto parts story- good luck

hi it can really only be two things, first is the fuel sender on the pump inside the tank it could be stuffed or sticking causing a false reading, second it can also be a faulty fuel gauge on the dash.

THIS PROBLEM IS ONLY CAUSED BY ONE THING, AND THAT IS A DEFECTIVE GAS GAUGE SENDING UNIT IN THE GAS TANK

Most likely problem is a faulty sending unit. Bad news... it's inside the gas tank.

Your sending unit inside of the fuel tank is probably faulty. Unfortunately you have to drop the tank to change it.

When gauge is pegged at full, usually means a bad ground. Check wires at fuel tank, wiggle around, maybe one came off. The bad news is it is hard to get to without removing the tank. Sometimes you can reach arm in and get to them. Also check body ground at read of van.

The float that helps detect fuel level is most likely broken. You or a mechanic will have to remove the fuel pump from the gas tank and check and possibly replace the float. Merry Christmas.

no im not sure why they would do this
just to make sure they fix it.
did they test it or just give you an estament?