My dad's caravan with almost 95,000 miles has had issues for a few months when in reverse. It start out being kind of jerky going backwards, and now it can't go up hills in reverse and the throttle seems to do nothing to make it go faster. There was a code for an issue with the VSS so I replaced it which seemed to make the issue a little better (but really could have just been a placebo) but it didn't go away completely. I tried disconnecting the battery to reset the controller as suggested on a thread where someone posted about having a similar issue. The trans fluid has also been changed since the issues started happening, and it now has the same code about the VSS as before. What else can I do from here to try to diagnose the issue?