2010 5.7l tranny issues?

This just recently happened on my 2010 tundra and is starting to become an issue on this long weekend. When in my drive way and shift from park to drive it wont stay engaged and pops back to neutral. if i try and go to sequential shifting it wont even engage. to go any where i have to hold the automatic transmission in drive position just to limp it around. are these transmissions still a linkage design? i havent crawled underneath yet i am going to spray some of the mud from underneath the truck and see if something is binding but any help would be greatly appreciated.
Thanks