2007 5.9 Shifting funny
 

My 2007 is shifting funny. 1st through 3rd are fine, but then it sounds like it just falls into 4th or O/D. Also, when running up a slight incline sometimes it cant decide what gear it wants to be in. It will downshift and then immediately upshift again. Sounds like its slipping sometimes, but Im not a dsl mechanic. Im just wondering if there is anything I can do to troubleshoot. Fluid looked good and full...

Thanks