I have an Uplander that has not been driven much over the last year. I am getting ready to sell it and I noticed that the transmission was not going into reverse easily. It would eventually go into reverse. It also wouldn't go into drive readily. It also seemed to slam into gear when going forward. I changed the transmission fluid and things are better, but there still seems to be some reluctance when going into reverse. What could be causing the problem? Is there anything else I can check myself?