D-Spark would definitely work in your case, as its stim-free. If your goal is endurance I might even give sarms a try, particularly cardarine 20mg/ed (10 in the morning, 10 in the evening).
I would go with a proper meal 90 minutes before training and toss in some DSpark when it's back in stock. I use Cardarine sometimes on training days and dose all 20mg 30 minutes before training. It gives me a good boost.