You might mention the brand of rifle, the caliber, and the model you purchased. Many times there are forum member that own the same model rifle and could give you some excellent advice on loads to try.

In the mean time, Goex is a great powder. No need to change at all. Start your testing at 90 grains of 2f and a good quality bullet and sabot. Because of the size of the deer, you might look into Shockwaves in the 250 class which should offer good penetration and long range shooting abilities.

If you suspect your shots might be closer, again with the 90 grains of Goex try something like a .430 .44 caliber 300 grain XTP or Speer Gold Dot in a Harvester Crushed Rib sabot. These I find normally accurate in most all my rifle.

If you want range, knock down, expansion, and just excellent bullet performance, consider the Barnes Expander in 250 or 300 gr. Also the Nosler Partition in 250 grain (I believe they are). Some others are Parker Ballistic Extreme in 250 grain. All of these should shoot real well, and if more powder is needed, these can take a much larger powder charge and still give excellent accuracy..

This is going to be a lot of trial and error for you at first. Once you find a good load, remember it. Then the fun comes with playing with different loads, sabots, and bullets.

Good luck with your new rifle.