I get gold pretty much every time I fly this. Its one of my favorites. I do it often, but a bit differently...
Go straight ahead and take out the center and right gun. Ignore the left gun for later.
Go take out the first cow. As qrook mentioned, take out as many troopers as you can before hooking on. Once you hook on, make your cable run at FULL SPEED. You can usually just stay turned, but I usually straighten out for a split second on the sides to avoid hitting the legs.
Now head back to the dam and take out the guns by the shield generator. Shoot from a distance; a miss will either take out the bunker or hit the generator. As you get closer, take out a few troopers. But don't make yourself turn before you hook onto the next cow and take her down; time is of essense! Not only do you need to get all the bad guys before the pigs cross the dam, but there are lots of things to wail on you if you hang around here.
Then head over to the third cow and wrap 'er up. She truely won't "say boo".
Now turn around - that third gun is right behind you! Take it out, head over the hill, and take out the gun next to the research center.
The way I play it, I will have been hit, at most, once or twice by now. Which is good, those tank droids are swarming. Waste all the tank droids, and shoot down the bombers (you'll need the kills).
Take out the shield generator, and then start wailing on the research center - you should have taken out all the guns and a few wandering soldiers before the AT-PTs "have arrived". Get the bonus, finish off the research center (make sure to kill everyone there!) and you're done.