The CTS2 will be as accurate as the sensor is. It's reading that value straight from the PCM. That sensor can go bad, though. What does it look like compared to your coolant temp when the engine is dead cold? They should be within a few degrees of each other before you start the truck.
With all of that said, depending on conditions, 220-225* isn't out of the realm of normal. I don't really start to worry about mine until it hits 230*.
A better tell of oil cooler health is comparing the split between EOT minus ECT (commonly referred to as the "delta"). I'm pretty sure there's a TSB you could find that covers the exact procedure. But, essentially, you get the truck up to operating temp (192*), then drive it at 60-65mph on level ground for 30+ minutes. Do a couple of full throttle runs, and pay attention to your max deltas. Your oil temp should never be more than 15* higher than your coolant temp at any time during that procedure. If it is, you've probably got a clogged oil cooler.
Maybe someone can chime in with more info on the exact procedure, or a link to the TSB.
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