It may be called hard mode but it is incredibly easy and the only chance you will die is from falling while platforming. To make it even easier you can spend Sheriff Stars on upgrades that increase Rango's health and his weapon performance. You can buy upgrades from a salesman who is found throughout each level.
To collect all of the collectibles please use the guide found HERE. (Credit to NiteJokester) You may have enough Sheriff Stars by the end of the game to buy all of the upgrades, if not please see the "Red, White & Blue Sevens" achievement for a good Sheriff Star boosting method. As soon as you buy all of the upgrades this will unlock but you have to have completed the game and collected all of the collectibles as well.