It's important to note that tripod/head weight ratings are typically not directly related to camera weight. Confusing but true! The problem is with the weight distribution of your camera and lens and how the tripod/head area positioned.
A small/short lens on the camera is going to have a very different center of balance than a big/long lens on the camera. It's likely that the big lens is heavier, but even if a big lens and small lens are the same weight, the weight distribution is different -- the long lens is going to more the center of balance. The camera's tripod socket is always in the same spot regardless of how long or short the lens is.
Mount the camera on the tripod so that it's level. With a Gorillapod (small compared to a full-sized tripod) switch to a long lens and I bet you can feel the center of balance change and the weight pulling down on the front of the lens.
Point the camera up, say at 45 degrees. The long lens feels better balance over the center of the Gorillapod. However, now switch back to a small lens and you'll feel that the back of the camera is the heavy part and pulling on the Gorillapod.
Of course, neither of these examples touch upon the problem of drifting. The uncentered weight of the camera/lens torque the head/legs because they aren't rated highly enough to handle the load.
Simply, I'm not at all surprised to hear that you're having some trouble and need to step up to (at least) the SLR model. But, if you're looking to use this with any regularity I suggest looking at a full-size tripod.