A noncreature permanent that turns into a creature can attack, and its {T} abilities can be activated, only if its controller has continuously controlled that permanent since the beginning of their most recent turn. It doesn't matter how long the permanent has been a creature.

While it's a creature, Gruul War Plow gives itself trample.

While it's a creature, Gruul War Plow has creature type Juggernaut. It doesn't have any abilities associated with the card named Juggernaut.