Hi Tom and all:

The microphone gain cannot be changed from the menus or with an internal 
adjustment.
To change the gain or adjust deviation, one must go into the service menu.  To 
do this, a ps2 cable must be plugged into the data jack on the rig and two of 
the pins shorted together.  When the rig powers on after this, a service menu 
appears after a few button press combinations.
Probably a little more PITA then it is worth.
All I can suggest is perhaps placing some thin tape over the pin hole where the 
microphone element is inside the mike.
It is odd you have a hot mike since all the tmv7a's i have ever heard or used 
have fairly low audio.
You are lucky to have one that you don't have to scream into and eat the mike.
There is probably a resister mod that can be done inside the microphone to tone 
it down a bit...but again, its a PITA.
Try some scotch tape over the pin hole first and see if that helps.
Nothing too thick because that would likely make the audio mufly.
73
Colin, V A6BKX and Rowan the ham dog