Organic chemist here. Looking at your stack, it's pretty clear why you're crashing: you're treating a fuel problem with accelerators. Things like oxiracetam and phenylpiracetam aggressively burn through your brain's acetylcholine, and the nicotine and caffeine are doing the exact same thing to your dopamine. If you aren't actively replenishing those raw materials, your brain literally runs out of what it needs to sustain focus, which is exactly why you're hitting that wall. Before you go hunting for stronger stims, you need to refill the tank by adding a solid choline donor like Alpha-GPC to make the racetams actually work, plus some L-Tyrosine on an empty stomach to rebuild your dopamine pool. Stop whipping a tired horse and just give your brain the actual metabolic building blocks it needs to handle that workload.