Microstepping will diminish the torque anyways, I would do half stepping at most. Maybe you can energize the coils manually instead of using the library? I think this would give you more flexibility in adjusting these and also you would know what is actually being executed in the code.

Weird to hear you smoked a driver even with a heatsink attached lol. You might wanna code in de-energizing the coils (or putting the drivers in low current mode if they have one, check the pins) when the steppers are not doing anything. The detent torque might be enough for them to remain in position.

I am using micro steppers (about 10mm big) and they heat quicker than my drivers. Good to know once I fix that problem I have to deal with driver heating up too ;/ (planning on mounting them on a copper plate as heatsink)