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...and the new beta firmware does not work for me. The 5DIII only fires lights a small proportion of the time. This is the case either using AC9 units to trigger Paul Buff monolights or using 550EX units on TT5. Before the firmware installation, both setups worked fine with a 5DII. We're not there yet.
Just to be clear, all testing was done with fully charged batteries, distances were small, there were no sources of interference, and I followed the recommended sequence of turning on the various units.
It won't help if I just say beta 6.153 is working fine on my 5D3, but since my setup is almost identical to yours, (TT1, (4) TT5's, (4) 550EX's, AC3, (4) AC9's, (4) Buff WL Ultras), I'll try to offer up a few additional things that might be worth trying...
When you installed the beta, after the utility did the reset, did you choose to import previous settings, or just start from scratch?
FWIW, I just started with the reset defaults and then configured C1 for my 1D3 and C2 as Auto for 5D3, 7D, and T1i. C1 I set the Hypersync/HSS transition at 1/500. C2 I set the Hypersync/HSS transition to Auto.
Make sure 5D3 is showing up as an option for the camera model. Try it both explicity as 5D3 and by trying Auto. Try both C1 and C2. Again, make sure whatever settings you configure are the same on the transmitter and all receivers.
Make sure you click the "Apply" button. And then wait several seconds for your PC to make the USB disconnect/reconnect sounds before disconnecting your TT1/TT5 and moving on tho the next one.
I was also very sure that all 5 devices were configured with the exact same settings.
Hundreds of shots so far. Not a single miss. I didn't even use fresh batteries.
FWIW, my power up sequence was 550EX, TT5, TT1, 5D3. Test shot to sync the transmitter and receiver. Then everything was good to go.
As I was going through and testing the adjustable settings, the shutter curtain was very predictable and consistent... I was able to get clean 1/250 xsync with the 5D3 and a very slight bottom curtain at 1/320.