If you look at heart rate files for CX and time trials, they're very similar -- 40 minute balls-to-the-wall effort. Power, on-the-other-hand, is very different as cross is anything but a constant effort.
Do you run at all? If not, that would be one good place to start fine-tuning your training. The runs are typically short and intense, but enough so that they can make your already high HR go even higher. You need to learn to be efficient during the runs and with your mounts, dismounts, and barriers. If you can be efficient, you can keep your HR in check.
Although you've only done two races, can you see a pattern of where you get dropped? Is it just after the runs? Or at the more technical sections? Or on the flatter power sections? See if you can notice a trend -- this will help you determine how to focus your training.
Cross hurts. There's no way around it. Even when you look at the pros, it hurts. That's what's so darn fun. XC races are much easier -- 2 hours of aerobic riding. CX is a short, hard, anaerobic effort.
Given all that, I'm training a bit differently this season than in past years.
I do one day of 2 x 20s on the bike (ie the TT effort). I run 3 or 4 days a week and include short intervals in all those sessions (30s and 60s). I spend at least two days riding easy and focusing on my skills and technique. And I'm lifting weights twice a week too. My on-bike hours are WAY down from what I typically train, but I know that I need to focus on some different weaknesses right now so I'm doing that. I miss my long rides, though, so I'm going to try to slip one in each week if I can.