I've been meditating for roughly 2 years, most of that is on-off bullshit casual meditation for 20 or so mins to deal with intrusive thought patterns. So, I was pretty much at stage 2(or so I believe) in that timeframe.

Recently though, in the last 2 months I've felt a real need for awakening,  so I increased my session time to 45 minutes and focused on consisntently and diligently trying to reach stage 3. (I know this isn't anywhere near some people's practise, but 45 minutes was the minimum reccomended time that Culadasa states in TMI so I'm just doing that for now.)

I'm pretty much at stage 3(?) now, but my awareness and emotional control feel light years above what I had. I can easily sit with feelings of unsatifactoriness and suffering, and my attention seems to naturally jump to awareness of my body and breath in daily life. Plus intrusive thought patterns have been completely eradicated.

Is this what anyone else felt at stage 3, or am I slightly further along than I think?

Stage 3 in TMI mentions dullness as a major obstacle, but I don't typically feel drowsy or sleepy unless I'm meditating while being sleep deprived. Meditating on a normal amount of sleep doesn't seem to have much dullness occuring at all? So am I really at slightly later stage like 4/5 without knowing it?

I wouldn't like to 'overestimate' what stage I'm at in TMI, I'm a neophyte meditator and I wouldn't want to claim attainments that I don't actually have, nor would I like to think of myself as incredibly gifted because I'm most likely not. But, if I am at a later stage, it might be good to start doing what Culadasa reccomends in that stage so that I may develop my concentration further.

I meditate with eyes open, if that's relevant. It seems like the only factor that may lessen the dullness I experience.

Yes, I'd say the difference is that pronounced.  Remember, Culadasa states that by the end of stage 3 you have reached a level of concentration that no normal person (non-meditator) could have attained. So if you are like me, and your natural level of concentration is rather poor, to go from that to a level beyond what any normal person can do is an extraordinary difference. 

dullness is more pronounced at stage 4, and even then I didn't experience it too badly. I didn't experience dullness in stage 3. 

It is OK, and useful, to try out techniques associated with later stages, as long as you stay focused on mastering the stage you are practicing now.

You did not say much about how well you are sustaining attention on the sensations of the breath, and whether those remain in peripheral awareness when attention strays. That is a key measure of what stage you are in.

My breath stays in peripheral awareness when I am distracted, even when I am very sleep deprived I can still perceive it very lightly while my attention is elsewhere.

I'd say I am firmly in stage 3 now, although I have a very bad habit of going to sleep late and waking up at 5am to meditate which causes some sits to turn into me just trying to stay awake.

But, assuming normal conditions, my attention naturally gravitates towards the breath and tends to stay there during a session.

I am not a teacher, but that sounds like stage 4 to me.