Chevy suburban won't go in forwards or reverse after changing filter in t

when transmission fluid is changed, sometimes it takes a long time for the fluid to get circulated properly. If you had replaced fluid under pressure, it might have helped. I had a similar problem one time, older vehicle. It wouldn't shift after transmission fluid and filter change. I was about ready to junk it, took it out on highway, one last time, and boom, it shifted. Worked fine afterwards.