The gear change effect is one of those that will really highlight anything suboptimal in your setup.
This is for several reasons. In several of the more accurate games like iRacing, the duration of a gear shift effect is actual based on a model of the transmission. It can be quite brief. You need a well matched amplifier and transducer to react in time and with enough power.
I've never used your particular amplifier or transducer. I tried to find some details on them but didn't find a lot. The amp seems to be discontinued. However, I did find an article about it that is concerning.
"Low-frequency 30 Hz or 50 Hz filters prevent infrasonic sounds from making their way to your woofers. Sounds below this range are all but inaudible to the human ear while simultaneously requiring the most energy to produce. A filter will prevent an accidental tap of the microphone, for example, from reaching the rest of your system."
This would indicate that the amplifier has a feature that is removing some of the most important frequencies that you would want to feed to a bass transducer.
I looked at the MBQ-1 specification on their website but there isn't enough info to make a determination on the frequency range of the transducer or wattage needed to drive it.
At a click look, I can't say whether your amplifer and transducer are well matched or if your amplifier or transducer are suitable for SimVibe.
Given that you've already invested in them, here are a few tings you can try:
Try changing the frequency range of the Gear Shift output. The default is 45Hz. According to the article I found on your amplifier, it will try to filter out a 45Hz output. Maybe try something around 25Hz and see how that works out. You could also try something above the range they filter, which the article I saw claims to be 55Hz. Perhaps 60Hz would do better with that amp.
You might also check to see if your sound card has "special features" that are detrimental to bass transducer performance.
The last idea I have is to try adding a tone smoothing filter to the effect. I haven't tried this, but it might extend the duration of the effect a bit. The higher the smoothing level, the more it might elongate the tone.
I don't have any other ideas at the moment. I don't think the effect itself is broken. We use ButtKicker Mini LFE's here with an eMotiva amplifer and a basic Sound Blaster Audigy PCIE card. The gear shift effect is always pretty noticeable with a default profile.