Have 2000 pontiac sunfire runs fine as long as gas guage reads full as soon as it drops between full and 3\4 starts to run rough when accelorating or drive along acts like it wants to run of gas the

There is a good possibility you have bad gas. The fuel will separate and once you reach the bad stuff, your problems begin. You need both a fuel pressure check and a fuel sample done. You periodically need to replace fuel filter and this would be a good time to do it.

There can be a part called a fuel pressure regulator which is suppose to provide an even flow of fuel and compensate for tank volume. It may be bad or messed up from the bad fuel.

There are a few pressure gauges you will need and the knowledge in using them. The easiest test is the fuel sample test and some of the pressure gauges may be loaned from Autozone, Advance, or Oreilys autoparts.

I have seen this kind of problem before. You will have to get access to the fuel pump. Some cars have an access under the rear seat. Most don't, so you will have to lower/remove the fuel tank and the locking ring on the tank that secures the fuel pump/sending unit. You may see obvious signs of a problem, like a hose loose, but i recommend that you replace the fuel pump/sending unit even if you don't see a problem.