What is up with all this weight talk as if it is the #1 issue here? You ran a 2:54 and people are acting like you are at your capacity for training improvement. Of course weight would help, but honestly training would help more than weight at a 2:54.
I ran 2:21 at the start of the year at mid 160s (who actually knows what weight you are anyways? Taper, carb load, pre-run, pre-bed, etc). I am a hair shy of 6'.
I'm impressed by your consistency and lack of injury. I don't know where you are most limited, but generally you are likely limited by a slew of things, so please consider some training advice:
1. Get a coach if you have the money. They are much more knowledgeable than these boards (as entertaining and fun as they can be).
2. Increasing your training volume. Note that I don't mean your total MPW. Slowly make your workouts longer (don't forget to take down weeks occasionally while increasing).
3. Train at a variety of speeds. Yes, specific training at the end of a cycle seems like the right thing to do. Before your get there train your cells to process various amounts of lactate and various duration of time under stress.
4. Maybe increase your MPW. Most people do better for the 'thon in triple digits. Not all. Figure out how you respond. And I don't mean over the course of a few weeks. It might feel terrible for a bit.
5. Read about fueling for your runs to get the most out of them and also recover as quick as possible.
6. Focus on being fresh for your next workout. You need to be doing body work to make sure you can handle the increased load. Everything from core work, lifting, to self massage. This is also injury prevention. You need to be strong before you can increase your training volume.
7. Don't sell yourself short. Set a hard but obtainable goal and get there.
Probably lots more, but rattling some. Hope this helps.