Before you start checking resistances at the wiring harness connector, let's back up a step to the easy stuff. Is the check engine light on? If so, have you pulled the codes? If no C/E light is on, and/or no codes for electrical components inside the transmission, then I would not waste time changing out the wiring harness, or solenoids. Chevy's are pretty good about popping a code for electrical items within the trans. *Usually* the absence of codes for electrical problems inside the trans leaves you with mechanical issues. Please note I said *usually* as there are exceptions to this.. Many, many, exceptions.
Can you tell us exactly what the trans is doing wrong, or not doing right? Pull codes, then let us know what is happening with the trans and we can help you from there. Also, how many miles on the trans? What color is the fluid & what does it smell like? What is the fluid level?