When I attempt to calibrate extruder steps the increased values don't correspond to physical increases
Mechanical?

You basically answer your own question that there could be a mechanical issue.

If 93 steps gives you 38 mm, to get to 100 mm, you need to divide 100 by 38 = 2.63 times. This implies that you need 2.63 x 93 = 244.7 steps/mm (not 149.73).

You even tried close to 400 steps per mm to see you are not extruding 100 mm of filament. This implies that you are either missing a lot of steps (increasing the stepper current or increasing the temperature of the hotend would help out) or the extruder gear slips on the filament (increasing the pressure on the extruder gear and filament could solve this).

Or not mechanical?

Furthermore, it could be another issue than mechanical. If your extrusion rate is too fast, the stepper might not be able to cope the high speed and miss steps. I have had this before with a too high of a retraction speed.