Why does a 2015 Cummins QSB3.3 in a JLG telehandler blow white smoke and lose power under heavy load?

[USVeteran]

My JLG telehandler with a Cummins QSB3.3 runs fine most of the time, but under heavy load, it suddenly blows a big cloud of white smoke and loses power.
Fuel filters were recently changed, and it normally runs clean except during the issue. Could this be an EGR, injector, turbo, or coolant-related problem?