Time Trial / Time Trialling / TT

Am I going out too soft? - http://app.strava.com/activities/71495831
It doesn't make sense to me that I'd be able to finish a 23:45 going uphill at 26mph+. It could be the method that other regular riders of that course have but I've previously had a 2min man catch me on the 6th mile only for me to pull away from him for 15seconds. I've also had people say that they've been catching me to the turn then can't make any ground on me afterwards.

Hard to tell without spending time in a lab estimating your aerobic threshold is in terms of output watts by monitoring lactic acid levels, blood sugar levels, oxygen consumption...

By "pull away from him for 15 seconds" do you mean you end up only losing 1:45?
Could be someone heavier but more aero getting an easy downhill ride to the turn but not having the output to beat you on the way back.

When was the last time you did a TT and actually hit your limit before the last mile? Do that, then ease off each week until you hit it with 10 metres to go.