Bad gas Mileage

My 95 astro gets about 12 Hwy Miles and 8.5 City i've change the fuel pump and injector sometimes it runs real smooth and sometimes rough. sometimes I have a problem going up hills. can someone please help :banghead:

Does the "Check Engine" light work? Does the "Check Engine" light come on or stay on while driving? What tune up parts, (and brand) have been replaced, and how long ago? How many miles on the vehicle?

the injector was replace about 6 months ago AC delco part the fuel around the same time generic brand. I have over 230,000 miles. you can smell the fuel somethimes coming from the exhust.

Check the fuel pressure, here is a guideline:

Fuel pressure is not monitored by the On Board Diagnostic (OBD) system and therefore cannot set a Diagnostic Trouble Code (DTC), or illuminate the Service Engine Soon (SES) light.

Fuel pump operation:
The fuel pump circuits are designed to energize the fuel pump through a relay continuously any time the key is in the START position. When the key is in the RUN position the fuel pump will operate provided the engine is running. If the engine stalls, or is not running for any reason, the PCM/VCM will shut off the fuel pump approximately 2 to 3 seconds after the key is turned to the RUN position.

Fuel pressure test:
Install the fuel pressure gauge to the test port near the distributor. Turn the key to the RUN position but do not start the engine. While the fuel pump is running, fuel pressure must be 60-66psi. After approximately 2 to 3 seconds, the fuel pump will shut off. Fuel pressure must remain between 55-60psi for several minutes. A drop in pressure below 55psi indicates a leak. The most likely place is the fuel pressure regulator, or the lines under the upper intake manifold.

Here is a link to an inexpensive yet ample fuel pressure tester: http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=92699