my car was at like less than half a tank and then i filled it up, when i start the car, all my gauges do their sweeping thing, my fuel gauge included, then it goes to full and runs back to empty and my check gauges light comes on, but it doesnt show anything like my gas tank or anything, so what is the problem?

Mine did that and it was a bad fuel sender sensor.

Ditto. You described my issue to a T. I dealt with it for a year then swapped out the sender and fuel pump for fresh AC Delco parts this past summer. To the tune of $425 (and that was from GMPD).

In the mean time I was using the trip odo to determine my range.

Agreed... sender went south

I've seen them do that, then after some gas is burned off, return to full and operater normally. The sender had one bad spot at the extreme top fill (which would actually be the bottom of the sender sensor)

That was going to be my guess. Run a few miles on her and see if E doesn't also stand for "Excessive Fuel in Tank".

At first mine did go back to F and then operate properly. That lasted for about 6,000 miles.

Then it would lay buried on E for the first 55 miles. Then it would go back to F and stay there until my next fill up. It acted this way until I swapped it out.

Same thing here, but it progressively got worse until the guage refused to work at all. Went for about a year and replaced the pump and sender this spring when everything rusted out and started spilling fuel all over, about 2" from the hot exhaust.

This has been discussed before, and there'* a technical service bulletin for it.
It seems to be a problem for the '92 mostly. I own a '92 SSE supercharged, and the gage did that on mine. I added the resistor as per the service bulletin, and now it still happens, but nowhere near as often.
Take a look at the following link:
http://www.bonnevilleclub.com/techinfo/?article=31

whatayaknow, this did happen on my 92 SSE :o