My transmission has been shifting rough lately. I have not changed the transmission fluid yet and it is dirty. It is not slipping but it shifts like it has a shift kit in it. I am afraid to change the fluid and filter. I have heard that sometimes if you change the fluid and filter it can make the transmission worse and cause it to fail completely. Is this true?. The fluid that is in there only has about 38 thousand miles on it. But i assume it has the original filter and the truck has 133900 miles on it as of current.