Well if you could pull a used injection pump from a pick and pull really cheap. Take it home and submerge it in diesel fuel in a can with a lid. Just in case your current one becomes really excessivly problamatic at some point. This would not hurt. Easier to find when not required right away usually and cheaper.

Also either test or install a 0-30 pound liquid dampened fuel pressure gauge. In hilly area you want 19 pounds fuel pressure in the base of the injection pump. Make sure this way that you always have good operational fuel pressure.

Twenty five miles per gallon in your hilly area sounds reasonable. You have checked the level flushed and replaced the separate oil supply in the present injector pump?