I doubt that it is a filter problem, but it is always a good practice to replace filter as first step in diagnosis to rule out that possibility. You really should have the codes checked to point you in the right direction. When it jumps out gear, does it happen in both forward and reverse? If you hold reverse lever in position by hand, will it continue to move? If it continues to move if holding it in, then most likely the detent in the lever has failed. The detent is not serviceable, so the whole lever needs to be replaced. If it will not continue to move when lever is held in, then you may have a bad pressure sensor. There is an enable sensor and a system pressure sensor. Both can cause the issue. As I mentioned before, checking codes is important to help diagnose, there are many other things that can cause the problem you are seeing, but the things I mentioned are what I have seen most often.