What Automatic transmission does it have? Most likely it is an Allison AT540 series. Not the best choice as they are only rated to about 22K gross. And are marginal at that. The one thing I have learned since becoming a medium duty owner is that a manual transmission is the best choice. Next would be an automatic with a lockup torque converter and overdrive. The AT540 series Allison is a non overdrive, non lockup torque converter transmission. In my truck the cruise rpm is 20 to 25% high because of the inefficient torque converter. I have another post describing the change over I am making to an Eaton-Fuller 6 speeed.
As for turning up the power, The DT466E is an electronic controlled engine. Any power increase would have to be reprogrammed at an International dealer or there are a few aftermarket programmers available. I don't have any personal experience with them. The International upgrades are pricey and they may require other upgrades on the truck to handle the additional power output.
The 195 HP rating is more than enough to do what you are talking about doing with the truck. The motor makes plenty of torque in the rpm range you will drive it in. Trying to compare it to pickup truck HP numbers is not apples to apples.
My truck started at 175HP and I had it upgraded to 210HP and did not notice any major difference. And to do that International required a Fan and Fan drive upgrade as well as changing the drive shaft to the next larger size U-joints. Very expensive with 4 driveshafts on a 254" WB truck.