Preheat oven to 350 degrees. Grease a 9x13 cake pan and set aside.
In a medium bowl, mix together the flour, pumpkin pie spice, baking soda, and salt. Set aside.
In the bowl of a stand mixer or in a large bowl with a hand mixer, mix together pumpkin, sugar, oil, and eggs until fully incorporated.
Add the dry mixture into the wet mixture and mix well.
Pour the cake batter into the greased cake pan.
Bake for 25-30 minutes, until a fork inserted in the center of the cake comes out clean.
Allow the pumpkin sheet cake to fully cool and frost with the cream cheese frosting.
To make the cream cheese frosting: cream together the cream cheese and butter with a hand or stand mixer. Add in the powdered sugar and vanilla extract. Mix well.
Refrigerate any uneaten portion of the pumpkin sheet cake with cream cheese frosting.