Brendon, there seem to be some key words in your post: gruelling & struggle.
It sounds like you're trying to change so rapidly that you're having to fight yourself all the way (ie. part of you is rebelling).
I'd suggest
Progressive Training. For your 30-day trial do 10 minutes exercise per day - but make it
every day. Every day at more vegies and less junk than you would - but not so much it seems onerous.
For me, the 30 day trial is about proving to myself that I can do something. If you set the bar so high in the short term that you're overwhelmed you'll lose interest in the long-term.
Also, if you've been having a long term struggle with this, insisting that you lose 80 lbs by the end of the year is probably counter-productive. That's a huge scary goal. And if, by the end of the year, you've lost 40 lbs you'll be discouraged - when that's a great outcome!
IMO, don't focus on the big picture - set the goals nearer and smaller. Lose 5 lbs over the next month. That's not so scary. But if you do that - then keep doing that, you'll have dropped 50 lb by the end of the year! That's one heck of an achievement!