HIM training plan question - advice needed

Well, you should be a little tired.  Is it a pacing the workout issue or is a lack of sleep or is your muscles are completely trashed and unable to generate power?

If you think it is too much, I'd dial back the intensity a little and see how you feel.  

I don't think switching plans is going to do anything.  I think you need to manage your effort.  

Regarding what is enough.  Difficult question.  Enough is dependent on what your body can absorb and if you can't absorb what you are doing, you can dial back the training load or ramp it up accordingly if you can take more.  You can manipulate the load by managing the intensity and duration.  That is why I say changing the plan is not necessarily the answer.  Those templates are a guideline and you need to adapt to it based on your circumstances.  If you have way more free time to train and a desire and capacity to handle more than pick one accordingly (or the reverse).

my 2 cents.

The reason I make my own training plans is because no one online plan was designed with me in mind.  My strengths, my weaknesses, my schedule of work and other obligations, or my goals.

Don't be affraid to mix and match plans how you see fit.  Training basically comes down to consistancy.  Don't get all caught up in the details and worry that if you don't follow a plan exactly that somehow the whole thing is going to suddenly blow up in your face.  Lay out a plan that allows you to maximize workouts into YOUR schedule and you'll likely see success.

I'm training for my first HIM and also noticed a lot of variance across plans.  I'm therefore using something of a hybrid plan that fits my schedule, but my plan is fairly close to the trifuel plan.  I plan out each week on Sunday night or Monday (Monday being my rest day).  I often feel a bit tired, but just figure that's to be expected.  I know I need to get more sleep (silly job keeps getting in the way).  Recovery weeks are very important.

Good luck!

Depends on your goals, but honestly, if you want to plan that's going to give you better race results, the plan that leaves you a little tired more often than not, and sometimes really tired even over a few days, is going to be the better one.

Of course, if work or family makes training this hard a problem, go with the 'easier' one, but expect to get lesser results.

You don't get anything for free in endurance sports. Pros love writing about how they spent a season training with a lot more rest days and less overall volume with better race results, but what they omit is that they killed themselves with 30+hrs per week of training the 2 years before that and many years of 20+hrs even before that.  

If you're feeling 'tired' during the end of your workouts, it sounds like you're on the right plan. If you're so tired that you can't even make it through 3/4 of the workout length in a week, you should pick an easier one. Those tired, beat-down days are the ones that are the highest yield for improvement despite the fatigue.

I second the notion of making your own plan.  The 3x plan on BT is good for flexibility, but definitely do not be afraid to adjust from week to week, especially if you're tired, injured, or work gets in the way.  I'm also learning much like marathon training, recovery weeks are important.