fuel gauge not accurate

Check the ground going to the sending unit.

Also - on some GM's you can (have to) ground the purple wire going to the sending unit quickly to re-sync the gauge. I would not use a direct short but something like a circuit tester light.

Finally - what do you mean by pegged to the right? Some GM gauges will go all the way around such that the needle is at the 6:00 position. If this is the case you have to rotate the needle back around manually. On some models, you can use a straightened out paperclip through the hole where the trip meter or odometer reset is, and gain access to rotate the gauge.

The gauge is a voltmeter. There is no flow through the sending unit to ground so the meter pegs when power is applied. Turn power off and it goes back to zero. Go back to the sending unit and find where you screwed up.

Remember in 99 the fuel level sensor is an input to the PCM. Ground is supplied by the PCM. Showing full indicates one or both circuits open. Check terminal tension at fuel module.