I would say make sure you have semi up to date armor and weapons and really think about the ways you struggle in pve. Then with that in mind trait to beef up your weaknesses and benefit your strengths. Engineer has so much CC and can do really gewd aoe damage I have a hard time believing its not viable in the later levels. I would go Dual pistols for more aoe dmg or pistol/shield for some great control, make pistols pierce get precision get all the chance to crit condition stuff and then trait to be more survivable after that. Supply crate for an elite and med kit for its heal then area heal combo when you destroy it. id do flamethower elixir gun and something like rocket boots. Crazy amounts of aoe dmg burn down a number of mobs, and make sure to grab speedy kits so you never get touched