My transmission works great from the minute you start the engine if the outside temperature is 60 degrees or greater. When it is 40 degrees and lower, the car needs to be warmed up and a slight revving of the engine (1500 RPM's or so) until the trans engages. Once driven and warm the trans is fine.

It was rebuilt 10000 miles ago and the rebuilder thinks the filter may be partially blocked. Thoughts?