Ever since I upgraded from Hitfilm 2 Ultimate to Hitfilm 3 Pro, I have experienced random crashes that weren't present in HF2 at all. I have tried to find a pattern or triggers to this, but I was unable to do so. Once I even just created a new project and tried to save right away after that and it crashed on me. Other times, it works fine for a while no matter what I do. But I have rarely ever managed to work for over half an hour without running into a crash. I have uploaded most dump files using the inbuilt reporting thing, I hope you can find a pattern in there.
As for hardware specs, here's a dxdiag dump: https://gist.github.com/MrManny/a95cb6d6d3cac6dc4026
And here's the tl;dr: Intel Core i5-4670K, GeForce GTX 760, 16 GB RAM, Windows 8.1 x64, drivers should be up to date.