What is the difference between an I/MM, E/MM and H/MM package?
When I see an "I" suffix on a part I can usually guess it indicates a part qualified for the "industrial" temperature range, and sure enough that's what it indicates on this part:



Incidentally, I had to go to microchip.com and download the "High-Temperature Datasheet" to get this information, as the H suffix wasn't listed in the datasheet at octopart.

Sometimes a part qualified on a wider temperature range might be restricted to a narrower voltage, like you found for this part. You'll need to review the high-temperature datasheet to see if the H suffix has any performance restrictions that affect your application. The fact that they issued a separate datasheet for it rather than revising the main datasheet implies there's likely some differences in the performance specs.