It has been talked about but there is too much modification involved, hardware and software. Not all factory trans are crap, the GM 480le I believe it is, is capable of handeling loads of power, and so does the Ram Diesel trans. The 545 has a major flaw in the design by using weak clutches in the 2P and 4th gear clutching. This combined with rediculous coding is a recipie for disaster.
I'm not sure what the 480le is but the 460le is in LS1 camaro's I believe. It is an ok transmission but it too fails with additional power. My buddy has a camaro with an ls1 and with just some bolt ons and a tune the trans started slipping.
Like I said, the transmissions are good for power levels they are designed for. If you add 100lb ft to the input shaft of most factory transmission it will likely have issues. I believe you'll see the same thing with the new 8 speed.
And comparing diesel to gas is not a fair comparison. Diesel's have to be able to withstand significantly higher torque levels than gassers.
It's pretty rare you hear of a failure of a 45rfe/545rfe/65rfe unless it's supercharged, turbocharged, or running nitrous.