"The effects of changes in serum potassium on cardiac action potential duration, pacemaker rate, and arrhythmias can appear somewhat paradoxical if changes are predicted based solely on a consideration of changes in the potassium electrochemical gradient. In the heart, however, changes in serum potassium concentration have the additional effect of altering potassium conductance (increased extracellular potassium increases potassium conductance) independent of simple changes in electrochemical driving force, and this effect often predominates. As a result, the actual observed effects of hyperkalemia include reduced action potential duration, slowed conduction, decreased pacemaker rate, and decreased pacemaker arrhythmogenesis."
"Agents Used in Cardiac Arrhythmias", Katzung's Basic & Clinical Pharmacology, 11th edition.
I have no idea what Step I considers correct; however, as I understand, you actually increase the slope of phase three with hyperkalaemia. This leads to a decrease in the repolarisation time and may contribute to the classic T wave changes. However, I have seen many patients who were rather hyperkalaemic and had no ECG changes that I could appreciate.