What were you readings? Is this a Mychron EGT probe?
I assume you have the probe in the tube between the header flange and the can. The probe should be inserted to the center of the tube as well. If you have both of these conditions you should be seeing temps up to 1180-1200F down to ambient.
The Mychron EGT probe reacts pretty fast so you should that reflected when working properly. You could take the probe out and with the gauge on wave a propane torch back and forth over it. If the temps go up and down the probe is probably good and there is something not right with the install.