"Almost too hot to touch" is about right for steppers! Particularly if you also use the "half current when stationary" setting, I wouldn't worry too much.

Current sounds low - I think I run my 3Nm steppers at about 3.something amps on the "crank it up until you can't rest your hand on them then wind it back a bit" basis.

Bit worried that you say you are using a series configuration. For best torque, parallel wiring is advised. As long as your PSU can take it (can supply enough current) parallel beats series hands down.

And if you are generating that much drag with the dust shoe, you need to do something about it! I've made mine adjustable by using a series of 1/2" or so plywood plates with small magnets glued in so I can easily adjust height to suit cutter length, etc. I managed to rip the bristle strip off mine recently due to a little accident and as a quick fix staple-gunned overlapping strips of plastic from an old milk bottle round the edge. Crude but effective! Strips are probably around 1.5" long to give flexibility when going over edges of work and so on.