I think I can answer all of those for you.

First... the clunk you are experiencing needs to be repaired before installing the Interceptor (I think you figured that already.).

You are correct in the diagnosis... Mode Switch. I've replaced 3 now (different VX's).

There IS a way to clean it and adjust it. If you want to go that route, please search for that thread. I like to make sure the thing won't fail for (hopefully) the duration of my ownership, so I buy new. (Totally your call).

Once repaired, if you install the Interceptor, you can induce a "similar" slamming effect by adjusting the POT too far one way... but when you adjust it right (lots of tune, drive, tune, drive...) you will get a result like the following:

Stock: revvvvv, shiffffffft, in gear.
Interceptor: revvvv, shFT, in gear.

(I know, my analogies are kinda strange.)

I hope this helps.
If you need further assistance or explanation, let me know. I have your same setup on my VX.

---JIM---