it's okay for the gunslinger class to change jobs early tho, in my opinion. Take the six-shooter you got for changing, buy silver bullets from einbroch, go back to payon dungeon lvl 1, and get enough job lvls for the skill bullet shower. After you got that, go to under prison ( try to rob the lady who dyes you clothes and hair- she will send you to under prison) and bullet shower the monsters there from as far away as possible, constantly moving to avoid getting hit. Pick up all the loot you can get your hands on to fund bullets and maybe grape juice, and before you know it, you will be lvl 70+ with minimal gears.
Pump up the dex as high as possible for this method, then some vit once you're doing enough damage.