My Cayenne is REALLY beginning to piss me off
 

2005 Cayenne V-6, 24k miles, I have owned her since new.

3 weeks ago I replaced a faulty fuel pump.

Today was my first refueling since the fuel pump replacement. I put in 20.2 gallons and the fuel gauge read 3/4 tank. I drove it 6 miles then added another 1.7 gallons (to the point fuel was overflowing). The fuel gauge still read 3/4.

Is it likely the dealer somehow screwed with the sender?
Any way to recalibrate the sender?
Any thoughts?

I can understand your frustration but from your writings it seems that a lot of the issue is with the folks working on your vehicle. They're charging you a pile of money to do sub-par work. Good luck with getting it sorted out. Owning a great vehicle should be more satisfying.

my CS never reads full, always a bit short.

OK problem resolved.

Apparently when the fuel pump was replaced a wire was not secured and it physically interfered with the float in the tank.

Cost to me $39 for half a tank of gas they needed to add.

The car and I have made up

Yikes. you think they would have caught that. I expect more of my Porsche mechanic.