I am having the same problem with my Saitek Cessna trim wheel. I am using Windows 7 64 bit, registered version of FSUIPC 4.934. FSX Acceleration with updates installed.
I have downloaded and used the latest driver for the wheel, not the software from Saitek, and can get the wheel centered, and it moves incrementally in both directions. When I go to axis assignments, the trim goes in increments in 1 direction all the way to -16380, but when I go the other direction, when it gets to 0, it jumps all the way up to +16380. If I click the reverse box, the same happens in the opposite direction. I tried to calibrate it using both the main page 1 and page 6 of the calibration section. I tried checking the filter box, but so far it has done no good. I have read and re-read the manual many times, followed the directions step by step. I have the joystick controls in FSX turned off, as I want FSUIPC to manage all my controls. The numbers I get in the calibration section shows -16380, +16380, -512 +512 delta at 256.
Has anyone found a new trick to get this working properly?
BTW, I also tried using the Buttons/Assignments section, but can't get the wheel to be recognized there.