Hopefully the float is just stuck somehow... this happened to me once, and I panicked; it fixed itself after a few days of bumpy roads... thank goodness.
Because; GM wants $300 for the sending unit!! GM doesn't want to sell just the sending unit, they include the mount for the fuel pump. They're all part of the same piece... but, supposedly, in the 80's, GM used a stainless steel wire for the sending unit's wiper to rub against. Over time, the SS wire wears thin, and snaps. GM went to a carbon fiber wire in the 90-up cars. So it was told to me that if I pulled a tank from a 90-up car, say, a Beretta, I could unclip the little rectangular sending unit resistor, and put it on my sending unit, in place of my worn out one.
Course, that involves dropping two tanks... and you might want to change your fuel pump to a new one while you're in there...
GM has one cool design feature of that sending unit/fuel pump holder, though. Looks like whenever fuel is added to the tank, the fuel "washes down" the whole sending unit. The inlet is aimed at the sending unit/fuel pump holder.
You might also want to "play" with adding an aftermarket fuel level sender to the tank. They're only about $20. But, you have to fabricate another opening in your existing tank... and watch out for sparks!
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-Tom P (Hot rodded 1986 Firebird 2.8l) | 
