New offhand is your cheapest upgrade followed by gloves and neck with +crit dmg instead of +attack speed.
Then i would go for a weapon with socket and +crit dmg.
You missing also average damage on rings.
If thats the spec you are using then its not enough for higher MP levels. You need something stronger as main damage spell then Firebomb. But there are allot of WDs spec guides so just look up them.
Vidrith is right about the skill set you have going on.
The DPS boost from pierce the veil is attractive, but if you're wanting to do higher mp levels at your current dps, you're going to have to increase your sustained damage output for elite mobs, and unfortunately PtV isn't the way to go about this.
First, I'm going to jump into your gear for a second here.
Your crit chance is starting to get up there, and that's good, unfortunately you have no crit damage to really back up those times you do crit. You're also lacking in average damage.
Average damage, Crit Chance, Crit damage, and high int will go a longer way than stacking IAS on a Witch Doctor. The reason being, is because NONE of our skills (outside of a zombie dog build) have any "break points" to meet, so Dot's wont "tick" faster over a given period of time, and pets wont attack faster either. You could say we're the slower, heavy crit and damage range focused int class of this game.
Now, I'm not sure what the EU Auction house is like, but a few things that I'm sure could be had for cheap would be to, replace the Litany with a decent unity and make up the all res in another slot. Replace the ias Zunimassa pox with one that has either some crit damage + average damage, or you can just do high int (120+) and say at least 35 average damage. Get gloves similar to yours, except replace the IAS with Crit Damage (would be a good idea to try and craft some). Replace your amulet with one that has Solid int, some Vit, Crit Chance, Crit damage, and average damage would be a bonus.
Note: avoid "Maximum damage" and target pieces with either xx - xx damage or minimum damage.
Fear not, if you don't have the gold to swap pieces, we can still make your WD be functional in the mp 4-5 range.
Welcome to the world of spirits, and one of the few passives that play nicely with attack speed, Rush of Essence.
This passive will make use of the 5 spirit skills in your arsenal, to keep mana incoming, for the times that you need to send out a quick burst of bears to knock down a big pack of enemies. The Tool-tip for Rush of essence isn't really complete, because it doesn't right out tell you that the passive stacks to hit upwards of 170 mana regen per second with every spirit skill you use, 4.9 mana regen at a time. Between that, and casting haunt on a couple enemies in the field, you shouldn't have any major issues with mana when you need to cast a steady stream of bears.
Your plan of attack with this build should look like this.
Spirit walk into a mob of enemies, and then cast Soul harvest, and proceed to mow down everything in front of you with a couple quick bears. From there you can tag a few enemies with haunt to get your 20.4 mana regen per enemy tagged + your 4.9 mana regen from rush of essence. Next, you can fire out a volley of spirits from spirit barrage dealing damage and yet again increasing your mana regen by 4.9 mana per cast, and follow up with bears whenever anything gets too close to you. You may have noticed the build doesn't have big bad voodoo, and the reason for this, is because of the 20% increased attack speed that the skill gives. You'd essentially break all the hard work to try and prevent you from going out of mana with the ias on your gear. Also, Mass confusion + Paranoia should do a decent enough job with it's 20% damage to the enemies in it's affected area :).
Hope this helps, sorry if anything seems a bit un-clear it's pretty late right now haha.
The post above me is basically the correct way to play WD.
Avoid AS with WD! This is your paper DPS only. WD's don't benefit from high AS. WHY? You may be hitting faster but not harder, also you spend all mana and can't sustain DMG for long time, which is needed on higher MP's.
So get rid of AS as much as possible, take crit chance instead.
Maybe you can get skorn with LS if you are dying too often.
I see you have purchased a skorn with LOH, you can't use that with bears. I said in my post to get a LS not LOH.
LOH does not proc with bears. Basically you have a unused stat on that skorn with this build. Acid is good with LOH but it is not good on higher MP.