I'm a newb to BOx, so forgive me if the answer is obvious, but the main IL2 forums seem to have been down for a week.

I'm using an MSFFB2, and in most of the aircraft there is insufficient trim available for level flight and thus i always need back stick pressure for level flight, which is frankly a pain in the ass.
Plugging in my old X52 there is no problem, so presumably it IS a bug with FFB joysticks, but i'm don't really want to use the X52 as it's a bit of a crude club of a stick in comparison to the MS.

Any fixes?

I use the FFB2 and don't have any problem with trim. There are two types of trim used in game, movable horizontal stabiliser used on German fighters and elevator trim on all other aircraft. These are mapped as separate controls.

Hopefully, this doesn't sound silly, but are you applying enough power at cruise to keep the nose up? It seems strange that only the up setting for the elevator is being affected. That's why I ask. If you were having problems with trim settings on all four axis I'd say you probably did have joystick issue. But, I don't know, doesn't sound right.
Not enough power will, of course, cause your nose tro drop. Even trim won't help. I'm no expert, just guessing. Try pushing the throttle forward a bit at cruise and see if you have an easier time maintaining your altitude.