2003 X5 Transmission Problem

[Stmary001]

Bmw 2003 x5 5hp24 transmission whining sound after oil change car runs ok for the first 1200 miles for my sightseeing tour after doing all that work on it. Then it start a whining sound louder when cold and slower to shift into gear.i check and recheck the fluid level and there is no leaks. I used Febi filter and Pentosin fluid.Feel like the fluid circulation is very poor.Being checking trying to get information on the problem and are told that Filtran filter is the best to used where would i get one.Does anyone have a solution to this problem of the whining and .Question (what the best tempature to check the transmission fluid)your help will be appreaceted.