I am not sure what is going on with the fuel in my 90 S10 P/U. The gauge has not been registering correctly. I assumed that if I put $20 in the tank and it only registered 1/8 tank, there was actually more. But as soon as it hits the E, it runs out. I have to nickle and dime it to keep it above the E even though I know there is gas in it. Tonight I filled it up (11 gallons) and it only registered 1/4 tank. There is no obvious leak and I smell no fuel. Even if the sending unit is bad or the float is broken, if there is gas in the tank it shouldn't run out should it?

Yes the sending unit is most likely bad.