Juggs have an easier time keeping aggro because they have an easier time with end mangemant.
First off, that's just laughable. Juggs actually have both worse threat generation *and* a harder time maintaining their resources specifically for the reason you mentioned.
To the OP, the first lesson you should learn is to never let your ammo drop below 8. As a Trooper, you have a resource with variable regeneration; the lower your ammo gets, the slower it regenerates. If you're running out of ammo, you're doing it wrong. Don't use Ion Pulse or Explosive Surge unless you're already at full ammo; keep Stockstrike, HiB, and (when you get it) Energy Blast on CD; open an AoE fight with Mortar Volley and follow up Pulse Cannon as they approach, then just setting into your ST priority (remember to keep your ammo up) to whittle your enemies down. Honestly, you should have no problem keep aggro as long as you don't gimp yourself by blowing through all of your ammo.