I have a 03' Durango with a 4.7 in it. I just pulled my fuel injectors to clean the ports (a tone of crap had built up in them). After reinstalling them and starting the car, there was a thin white smoke starting to come from underneath the valve covers. Thought it might be fuel that had gotten onto the block but it progressively got worse as the car ran. Why is it doing this?

How long had it been sitting? How many miles on it?

There's 105000. I did it 2 days ago but didn't have time to start it so it has been sitting for 2 days.

Probably oil getting on the manifold. You can either wash the area with engine cleaner, or take it for highway drive and let it burn off.