Hi Heather, that looks like the reg to me. If it was the firing valve/spring/hammer/spring then i would expect to see the chrono start with a number in the 770's and then the odd drop of 30-40fps now and again. Have you had it apart to give the internals a clean and quick check of the firing valve (pressed) o ring?
If you can get someone to bring the reg along to the Gathering on Sunday i can service it/set to 85 bar and get it back within a week. drop me a PM if you need any help at all.