The first image is of my 4th stepper driver. That blue plot where the signal seems to slowly decay from VCC is my concern. The 3rd Driver (in the second image, blue plot), doesn’t do that.
Does anyone know what this is indicative of? Is this a symptom of missing line terminating resistors? 
what signal line is the blue line? To me it’s a capacitance thing, or more specifically it looks like an RC filter.
The blue line is the return from the stepper driver slave out master in.
@Mr_John_Smith: SPI or I2C. Slave Out, Master In or MISO is an SPI concept and SPI does not need termination resistors, as far as I know.
I agree with @Brett, is sure does look like an RC filter. Do you have a shorted caps in the circuit?
…but then again, I am not an electronic engineer, so I am probably totally off the track here…
