MM Brake Problem

[redshift]

It seems I can only use drag brake with my MM to keep it from doing frontflips. Seems like I saw info on this, but a search came up dry.

The data-

14-ish pound custom running 3906 driveline (beefed, yes), 20/64, 9XL, 4S, MM, DX3.0.

DX3.0 settings- brake 50% R/B, subtrim zeroed

MM settings-
Forward-brake-reverse
Brake 0%
Drag brake 30%
Brake curve linear
Throttle deadband Average
Reverse throttle 80%

What I noticed on both the DX and the MM, anything above about 15% will throw the truck over itself quite harshly lol, and below 15% results in no brakes and also no reverse.

So I'm under the impression something is not right with deadband? The brakes are so aggressive that it seems like it's going right into reverse, bypassing any neutral zone.
Would changing my brake subtrim on the DX3.0 to a negative value? Or will that just give a slight pause, then still endo on me?

I want the dragbrake on zero, so I can coast when I want, also I don't really want anyone else driving it til I get this figured out, I'm afraid they won't remember to not touch the brake!

I tried to play around with the endpoint on the CastleLink brake graph, it won't let you move the 100% absolute value, I tried deadening the curve up to about 98%, truck still trips over itself, and as I said above, if I try changing the value on the basic settings page (the numerical value one), above and below 15% is all or nothing, respectively.

Any help is greatly appreciated!