Error message appears when I increase temperature of water, as the water slowly/barely trickles into the unit. Tried turning off the cold water, started the wash cycle, and the water did not come in at all. I also touched the inlet hose for the hot water, and I did not sense there was any water flowing into the hose and into the machine at all. Is that a inlet valve issue? Or some type of sensor issue?

That is a sensor issue but the sensor is built into the valve on that model so the water inlet valve assembly will need to be replaced. The valve you need can be ordered from the link below:

https://prismparts.com/products/whirlpool-washer-water-inlet-valve-pp6434826?_pos=1&_sid=59179a746&_ss=r