05 impala fuel gauge down around 7 o'clock 3.4 engine,sending unit ???

The problem you are experiencing is very common in 2000-2005 Impalas and many other GM model cars within those years. The gauges had defective stepper motors installed (1 stepper motor for each gauge/needle). Look up GM cluster gauge repair on internet. Your cluster can be repaired with new, upgraded motors for much less than the $400-600 dealers charge to replace your cluster. And if you find someone local that does these repairs, downtime is minimal. Good luck.

More likely the gauge cluster, have it scan tested by a mechanic. Scanner can run functional test.....sweep gauges! Depending on the scanner can also compare sending unit reading.....