really your numbers are meaningless. You need to post actual temps. Is the water at 195 or better or is it low? Do the 2 have similar values on cold start? ie. eot 75 ect 75 or are the numbers on a big split? once the engine is fully warmed up T stat open what are the ECT readings? Run at 65 mph level terrain if possible for approx 15 mins or more and see what the differences are. Should not be more than 15*. Also has your truck been tuned etc. Makes a difference.
If the tstat is not holding to temp ie open too soon you will get bad reading. So need to know actual numbers not spreads. Go to one of the truck forums for the best info FTE.com or powerstroke.org.
I know many claim casting sands but I have never had any in mine, and a lot of folks claim not have either. A big problem has been the ford coolant the 'gold' as it seems to gel when hot. Its possible a good backflush would help as would a better coolant.
I have 04 and just yesterday ran 150 miles and at 80 mph indicated only had 8-9 temp spreads, within 5 at 60-65. I have replaced the oem egr with a BPD unit and also a OEM oil cooler was installed.