Probably need to go to the hardware store and pick up some thick wall CLEAR vinyl tubing and a couple swivel brass fittings and one union. The fittings need to be the same size, as the fittings between the CAT fuel transfer pump and your truck's Primary fuel filter. {typically a #10 fitting and 5/8" tubing} (you are building a cheap sight glass, to look for bubbles, AND/OR watch what the fuel does AFTER shutdown of engine.)

I'll add some picture of sight glasses [= the "cheap design" is shown on a CAT 3116 engine.]

Get tubing long enough so it will reach a clean 5 gallon bucket of diesel fuel sitting on shop floor (like 3 feet or so)

Because your complaint happens quickly (1-2 minutes); you could start by sucking fuel, from clean 5 gallon bucket of diesel, with sight glass going into either your Primary fuel filter base(inlet side) OR the CAT engine's fuel transfer pump (inlet side) . Prime , Run, watch tubing to insure it is "full of fuel" ; then shutoff and watch clear tubing and see if fuel drains away.

 Note: (if you have the correct fittings, you could skip the 5 gallon bucket and just put the "sight glass/clear hose" in-between or in-line at transfer pump or BEFORE primary fuel filter base, also. Then prime, run and watch clear tubing/sight glass.

The basic idea is to "divide the fuel supply system" and monitor if the culprit is before or after the sight glass and then keep testing either towards engine or away from engine.

Edit: just to let you know, on extreme problems, I've had as many as 6 sight glasses on one truck before. (its problem wouldn't show up unless it sat 1-2 days)