You're right, it isn't easy to pick up on subtle hints at times.
Respiratory acidosis is a pCO2>45, regardless of the pH. If the pH is normal, then the acidosis is being compensated. Your body wants to blow off the excess carbon dioxide so tachypnea is an early sign. Along with tachycardia as the heart tries to increase it's output to meet an inadequately supplied metabolic demand.
Remember one of the important things about blood pH is that it affects the oxyhemoglobin dissociation. when the blood becomes acidic, the RBC has an increased affinity for oxygen and won't exchange gas at the cellular level as effectively. So if you have a patient that is ventilating well and complaining of "smothering", one of the first things to consider is an ABG. these problems are often vicious circles and the patient will continue to decompensate until we intervene. Because of this, the O2 saturation is often of little use because the hemoglobin is well-saturated with oxygen but it doesn't release it to the cells in exchange for CO2. Hence the build up in the blood reflected in the ABG.
Hope this helps somewhat, I'm sure someone else can come along and give a more complete answer.