fuel gauge problems

[MonzaRacer]

OK GM fuel gauge should operate on 0-90ohms or 90-0 ohms, I forget the actual direction, if you bought a gauge for gm the box/instructions will tell you. As for the sending wire from where you connect to gauge to wire at tank, both ends unhooked there had better be near 0 ohms resistance or the gauge will read wrong.
GM sending units go from 0-90 as the arm raises or lowers, again I forget the actual direction, (high to low or low to high). Also if gauge requires power and ground at dash, then quadruple check those as an improperly connected electric gauge will not read. Also generally GMS will read about 1/2 full with 5 gallons in tank regardless of model or year. Cars will sit on full for 200 miles then start too drop, actual reason is that a rapid change as you near empty "alerts" your "panic mode" to fill up rather than a car that sits at 1/8 of a tank and sloooowly hits empty and you sputter too a stop.
Sounds like either a feed wire or sending unit issue. near the gauge take the sending unit wire and ground it, from open to closed circuit is same as empty too full. unhooked it will read either full or empty, and go opposite when grounded.
One issue is using different resistors you can "test" the gauge.
Ford gauges ,iirc, use a 0-34ohm(dont hold me to this, mind may be playing tricks with my memory on ford specs) But I do know GM ohms max at 90ohms.