yes, your fuel sending unit is crapping out. Usualy you have to replace the whole fuel pump assembly. I know GM sells some stuff you put in your fuel tank thats suposed to help the connections on the sender get a good connection. Never had it work though, but we always tried it on cars that the sender wasn't working at all... might be worth a try... cheaper than a new pump assembly.
If not, fill your tank up and reset your trip odometer. Drive 100 miles and fill up again. take the number of miles you drove and divide by the number off gallons it took to fill up. Then multiply by I think 13 gallons for the amount of fuel you tank holds. then that is the number of miles you can go before your next fill up.
