What is the best additive? The transmission shifts a little hard sometimes. Its a new (rebuilt) tranny, that i just installed about 1500 miles ago. 1989 ford thunderbird, AOD
something that has been just rebuilt shouldn't need any kind of additive, take it back to whoever rebuilt or installed it and have them fix it, probably just an adjustment on the outside of the transmission.
No additives work if rebuilt you should take it back so they can check for leaks after seal seats. Plus it may need minor adjustments or fluid added if low.
You really shouldn't be trying to fix anything on a 1500 mile transmission with an additive. See if this is typical for the trans. I had a Dodge minivan that shifted fairly hard, they told me that was good, the more they slip while shifting the more wear on trans.
