I have 35's on 17" rims right now. I just want to swap the 35's for a set of 37"s I have and use the same rim. Would I need to get it re aligned?

 

No, the angle of the tire will stay the same if the alignment was ok before.

 

Any time you increase the size of your tires, you will be adding stress on the trucks suspension. I would drive it for a few hundred miles THEN have it aligned. You've invested a lot in the tires why not make sure they wear properly. Just my 2 cents worth.