When to Replace Injection Pump?

91 IDI, F350, 112K Miles, 4x4 Crew Cab, E40D, Banks Turbo/ Exhaust/Transcomand. My truck runs great, starts great. No issues. When should I think about changing out the injection pump? Do they typically fail completely (i.e. at once) or do they give you some sort of warning that they are starting to fail? I want to get my truck ready for another 7K mile round trip to Cancun, Mexico. I don't want it to fail on the road.

Thanks for your input!