I own a small business (20 people) and for 7 years, have been the sales force of one, doing all sales (quoting, follow up, customer service). The sales function took up about half of my time. Volume was increasing to the level that my responsiveness was at risk, so I hired an Inside Sales Manager 6 months ago. It has been my most liberating hire to date. 
The first 3 months, my workload was actually heavier, as I was training her. The 3 months after that I played catch-up on a backlog of important stuff that had been shunted aside in my prioritization of customers above most else. I'm now able to finally start digging in to "working on my business" sorts of things, and attacking projects that will take multiple actions over time, some of which I'll own and some of which I'll be monitoring my staff doing them. I LOVE being in this position, and started GTD in earnest about 2 months ago, to capture all this stuff and organize it for the doing.
When I wore the Sales hat, my "doing" was nearly all dictated by "as it shows up." Incoming phone calls and emails, most relating to sales and customer service provided me a constant work list, and I kept busy responding and keeping things moving. Thinking stuff as well as more mindless things like payroll, A/P, and analytical stuff (I'm still wearing the Controller/CFO hat) went into an "after 5 pm" stack.
Now I may only get 1 or 2 phone calls a day. And when I check my email on the same frequency as before, I often find nothing to do, or just a few things I'm cc'd on that require no action. So I have the amazing freedom to pick what I work on and when I work on it.
So given that I love being in this position, why is it so hard for me to break this habit, to move from doing work as it shows up to doing predefined work (or defining it)? By "hard" I mean "not natural." I'll go to my email, find nothing to do, and float for a bit, directionless. Then I have to talk to myself, saying "go to Wunderlist and see what you've starred." And while that is helping to focus me, I'm still easily distracted by a stack of checks showing up in my inbox to be signed, or a question from an employee that after answered gives me an idea of another project/action and I end up chasing that down for a bit instead of putting it into my inbox for later consideration.
Any ideas on how to yank my brain out of firefighting mode into working from my pre-defined lists without distraction?

The first 3 months, my workload was actually heavier, as I was training her. The 3 months after that I played catch-up on a backlog of important stuff that had been shunted aside in my prioritization of customers above most else. I'm now able to finally start digging in to "working on my business" sorts of things, and attacking projects that will take multiple actions over time, some of which I'll own and some of which I'll be monitoring my staff doing them. I LOVE being in this position, and started GTD in earnest about 2 months ago, to capture all this stuff and organize it for the doing.
When I wore the Sales hat, my "doing" was nearly all dictated by "as it shows up." Incoming phone calls and emails, most relating to sales and customer service provided me a constant work list, and I kept busy responding and keeping things moving. Thinking stuff as well as more mindless things like payroll, A/P, and analytical stuff (I'm still wearing the Controller/CFO hat) went into an "after 5 pm" stack.
Now I may only get 1 or 2 phone calls a day. And when I check my email on the same frequency as before, I often find nothing to do, or just a few things I'm cc'd on that require no action. So I have the amazing freedom to pick what I work on and when I work on it.
So given that I love being in this position, why is it so hard for me to break this habit, to move from doing work as it shows up to doing predefined work (or defining it)? By "hard" I mean "not natural." I'll go to my email, find nothing to do, and float for a bit, directionless. Then I have to talk to myself, saying "go to Wunderlist and see what you've starred." And while that is helping to focus me, I'm still easily distracted by a stack of checks showing up in my inbox to be signed, or a question from an employee that after answered gives me an idea of another project/action and I end up chasing that down for a bit instead of putting it into my inbox for later consideration.
Any ideas on how to yank my brain out of firefighting mode into working from my pre-defined lists without distraction?