How do i stop speed wobbles on my longboard?

okay so i've been long boarding for a while, and im fairly good, so the problem isn't me. i just got this new board a couple months ago, its the sector 9 sidewinder series Off the Wall 2. It has the double pivot gull wing sidewinder trucks which really give it a sharp turning radius and i have them tightened enough to where they don't get wheel bite. in other words, they're the loosest they could be safely. anyway, as soon as i get speed doing down a nice steep hill, i start to get what i think are speed wobbles. i haven't crashed yet but im worried that if i get enough speed it will be catastrophic. also, i found that it gets hard to carve when im going at a fair speed and i know i can do it. maybe im just worried my trucks are so loose that if i do try and carve sharp ill end up on the ground. they're double pivot trucks, so they're more complicated than normal trucks to tighten and loosen and ive already tightened them, but that just made it more easy to slip on gravel because of the amount i had to lean out. i just want someone to give me a few tips who actually longboards at high speeds like i do. no skateboarders unless you've had experience with longboards. thanks