I have this same slippery brake feeling when I come out of a carwash, and it does happen in the rain, but it's far less noticeable. Then again, I live in an area that's one step shy of desert, so the car doesn't see a lot of standing water.
I have the TCE 13" Wilwood kit in front and the 11.75" upgrade in the rear. I have Motorcraft pads in the rear (not sure what compound) and Wilwood BP10 pads in front.