Harsh reverse engagement

My 93 3.8 Trans Sport has developed harsh reverse engagement. Other shifts are normal. Temperature appears to have no effect - always jolts. Trans fluid level is OK (maybe a bit over). I was advised to change the fluid, which must be over 50k miles old anyway, and check the filter(s). I have no workshop-manual so can anyone point me to information as to where the filter(s) are and can it/they be cleaned or must be replaced? Is it a do-it-yourself job anyway?

Perhaps the advice I got was wrong anyway. Anyone else having this problem and actually determined its cause, please?

David Bytheway, Holland