Just bought my first gmc and am wanting to know a few things about it!  First thing that i'm wanting to know is what kind of oil is used in the gm products from the factory?  The truck that i bought is used and has 46k on it and i know what i like to use but dont know whats recommended for the 5.3 or if its just personal preference.  The sencond thing is that i noticed that when shifting up it shifts perfect but when slowing down and it gears down it gears down a little hard. Was wondering if they all do that and i'm not used to it or if its something i need to get looked at. Any help would be appreciated!
				
			
	