I'm looking a set of 33/12.50R17 gladiator x comp m/t tires but not sure if they will fit a 2007 stock 1500 mega cab without adding any spacers?

 

Stock wheels? 33 isn't a problem, the 20" wheels they put on them from the factory are 33". The width is probably too much for the rims if they are stock, it'll cause premature wear and they will look bloated. If they are not stock rims, you are not providing enough info - and likely won't get a reply unless you specify offset and width..

 

All about that backspace...