Lesse... First, YES, it should lock in solid and not move a hair.... Couple of things to check....

First, make sure your trim is centered, revo mix off, etc...

100% gain is actually too much... It won't make it wag with the 9254 cause it's so quick, but it does make it very hard on the servo since it has to correct so much... Drop it down to like 75 or so, should still lock in solid but be easier on the servo...

The big thing I've seen cause this is mounting on an inappropriate surface. Did you use the grey gyro tape that came with the servo? Sometimes if that still gives problems you can try doing gyro tape, thin balsa, gyro tape, then gyro... Bottom line, try mounting it differently.. (Using different tape, more or less tape, etc..)

Also make sure there isn't a lot of vibration in your heli.. If the blades aren't tracked, balanced, etc... Or even if your training gear is causing vibration, that can make it drift....

(you'll never touch the trim on a 401 once it's powered on... It'll read the "center" position when it inits, and after that you don't want the trim to change at all..