I know you’re a purist, but I highly recommend flash, regardless… try experimenting with a very little burst with high ISO. Part of the reason why you’re having low tonal range is because the light source in bars and such are not great for exposing your subject. For example, all those dim lights are sources that limit itself to a very low or eccentric color temperature. The flash bursts things at a perfect natural 5400 Kelvin, which is the same light temperature as sunlight. (ironic that you’re actually adding natural light with flash!) What makes 5400 kelvin special is that it provides the most tonal range for you to capture. You can use the best photo gear in the world, but if the subject to be captured isn’t in fine light quality, you wont have much to control anyways.

I also recommend experimenting your flash with gel filters. I think part of the reason you hate flash is because it brings the foreground with a strange white blast and render the ambient lighting tame. Try yellow gel or light red, or any you can get your hands on. The idea is to try to counterbalance the ambient light. For example, in incredibly tungsten situations, try light blue gel or light cyan. You don’t even have to flash your subject head on; just shooting upwards to the ceiling (if any) or any wall would act as an addition to ambient lighting.

Hope this helps; I enjoyed your drag series. Looking forward to your next works :).

Regards,
Chris