I ran the VIN thru Ford's data base. Obviously you are still under warranty, the first step is going to be to get the the dealer and have the system checked for any codes that may be stored and recorded. There are a handful of factory issued technical service Bulletins out there but none seem to be quite right on with what you have described. Once the scan is done any code that was recorded can be addressed.
This article supersedes TSB 07-3-11 to update the transaxle built date coverage and Part List.
Some 2007-2008 Edge and MKX, 2008 Taurus, Taurus X, and Sable vehicles equipped with a 6F50 transaxle with a build date prior to 10/21/2007, with any Output Shaft Speed (OSS) sensor or Turbine Shaft Speed (TSS) sensor diagnostic trouble code(s) (DTCs) P0715, P0717, P0718, P0720, P0721, P0722 and/or harsh engagements, no upshift, fifth gear only, could have an intermittent short in the OSS or TSS sensor.
Follow the Service Procedure steps to correct the condition.