G'day Mate,
Have you proved it was the radio? Did you do a range check? Did you check your switch, they have a nasty habit of failing at the worst possible time.
If the plane was coming straight at you from 70 yards away, was the engine in the way of the RF signal?
Was the Pitts using a gas engine, if so, it is recommended to use extra satellites on the RX, to see around lumps of metal, like a large gas engine.
6 flights on the Pitts, how much charge was taken out of the batteries on the first 5 flights, what capacity is the battery/batteries, I would always use 2 in a plane that size.
So my point is, don't be in a hurry to blame the radio, until all the above, plus a lot of other things including the batteries in the TX have been checked, sounds to me like you used that TX a lot, that day, but did you check the TX.
Sorry for your loss,