To earn this trophy you must use Salvadore's Gunzserk skill for a minimum of 90 seconds.
The only way to achieve this is to level up the middle skill tree, making sure to max out Last Longer
as well as investing in Yippy Ki Yay
The former will make Gunzerk last longer and the latter will allow kills to add time to the Gunzerk mode.
You will need to be a minimum of level 21 to have access to Yippy Ki Yay
but it won't hurt to level a little past that to add additional points into that skill.
Once you have the necessary skills, go to Frostburn canyon, or any other place with tons of enemies and simply keep killing until you surpass 90 seconds. Once the Gunzerk mode ends, you will have your trophy.https://www.youtube.com/watch?time_continue=197&v=O-lD07...