The IRCM doesn't dictate the temp the engine runs at, that is determined by the rest of the cooling system and the EEC. If you have changed the thermostat to a lower temperature without also getting a chip to command the fan on at a lower temperature then the engine will run hotter.
If you haven't done that, then make sure the fan is working on both speeds. 220 deg for the low speed, 228 for the high. The M usually coincides with close to the 228 deg. It could well be that your low speed fan isn't working.
Otherwise, clogged radiator, leaking headgaskets, air pockets, etc. are all things that can cause a hot running engine. Check the fan operation first.