If it is only the gauge- I'd rely on the odometer...
in all liklihood you have an in tank fuel pump so the gas tank needs to be dropped to replace it.
youtube will probably have a video of someone doing this job, you can watch and decide if you are up to it.
any autoparts store will have fuel pump- you may have to change electrical connectors
I did my 2001 gmc sierra a couple of years ago ( gas gauge long NFG- but pump was failing). on the pick up I was able to do myself- the trick on the pick up is to leave tank in place and raise the bed.
new pump was about $260- autozone
before dropping your tank, drain it.
if you have rust, be prepared to replace your tank straps