It's definately a stock IH pyro gauge. Some trucks have what they call a "gauge package" available as an option and I'm sure that's one of the extra gauges in the package. There's probably an oil temp gauge, boost gauge and maybe a trans temp gauge......just like the gauges we buy for our light trucks.
My 4800 had the option for a full compliment of gauges, rarely are they ordered, though. Most buyers just don't want to spend the extra coin for a package like that. Prolly costs $500 bucks.