757 VNAV Throttle Overshoots / Overspeeds

I spent literally hours (almost ALL DAY) with my QW757 trying to figure this out.

I have FSX installed on my main desktop rig at home and my laptop, for when I travel. My warthog joystick is very big and heavy and is screwed and wired to my desk, so for that reason I have a second joystick I use with my laptop when I travel. So having said that, I set up a flight testing scenario involving many VORS and intersections. This was from San Francisco (KSFO) to Charlotte (KCLT). I set everything up properly, according to the checklists, programmed the FMC etc. etc. Joystick software/firmware is up to date and they are properly calibrated.

On each flight, I made absolutely sure that when engaging VNAV, the throttles on BOTH joysticks were positively on idle- and remained on idle.

And the results are basically the same. OVERSPEEDS, over and over and over.

But I did noticed a few things: 1) This overspeed only occurs with VNAV (using manual speed changes are almost always dead-on) 2) These out-of-constraint overspeeds almost always occur when the plane is LEVELING OFF at an MCP set altitude or at Top of Climb. From what I have observed many times today, as the plane's pitch properly levels off, the throttle remains and doesn't throttle back which obviously results in the plane speeding up very quickly. Also, when this occurred, I was observing the throttle levers in the virtual cockpit. The thrust levers were moving, kinda like small flicking movement up and down. It looked like the thrust levers were trying to go down, but then it would jump back up. Then back down, then back up. I can make a video of it. It looked like the thrust levers were basically fighting themselves to go up or to go down.

Like I said, this is on two different computers with two totally different hotas joysticks.

Now, given the fact that the plane levels off exactly on time, right on altitude, the problem is clearly in the throttle. It's like it just gets hung up and can't decide to go up or down. I can't see where it's hardware related since I tried two totally different independent systems. It has to be something in the aircraft. I've been working on this for about 7 hours now, so let me know what you think.

Extremely frustrating

And here's a video that shows exactly what I'm talking about:

https://www.youtube.com/watch?v=z5fYFR4DM1Q

I didn't watch the whole thing, but my first observation is 320 seems a very high climb speed. I would expect something closer to between 280-300.

-Pv-