You're weapons will continue to be outdated until TVHM. Sal is the hardest to use imo since he is the only one who's action skill is entirely dependent on how effective your weapons are.
He won't truly shine until max level with max level weapons.
What is TVHM?
And ok. Just seems some missions are difficult.
True Vault Hunter Mode, basically playthrough 2 which leads into 2.5 where everything scales to 50. It's difficult because of his weapon dependency. You'll constantly find new weapons only for them to be useless in a level or so. Occasionally you'll come across a weapon that can last you quite a few levels though.
If you need help at all hit me up, my GT is ForgedSentinel.