My transmission is shifting inconsistent. on 2004 Nissan Frontier

It has 180,000 miles and is an automatic trans. I changed the fluid in it about 40,000 miles ago but not the screen. It shifts through the all the gears by the time I reach 40 mph. It starts to shake a little until I pick up enough speed to bring the RPM up. It seems to do okay after that. It does fine when I dont have overdrive on. I dont know if it needs fluid and screen changed. It may be a switch are an external problem I was told. Any suggestions appreciated. Thanks

Asked by for the 2004 Nissan Frontier
it could be a lock up issue by how u explain. seek free diag at aamco then shop the est