Power coolant flush: associated issues with it like drop in engine performance?

First - power flushes are not a great idea if there's no cause for it. A drain-and-fill is fine, unless you're coping with a restriction and corrosion issue you're trying to eliminate. You can create concerns if it's not necessary to perform. So, it's really impossible to know what is happening. A hands on inspection and assessment of all things related to engine performance -- including engine temperature as controlled by among other things the engine's thermostat -- is needed. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops