Just ordered a pillar pod for my 2nd gen diesel truck...........What would be the top 3 gauges to install?...I'm leaning towards Fuel pressure 1st, Trans temp 2nd and EGT 3rd.

Do you have a boost gauge in the dash? If not, it would be a toss up for Boost or Fuel Pressure.

No boost gauge, but I know if fuel pressure gets way low it can eat up the vp44 lift pump in my Cummins diesel.

Yep, you are correct.
But it's also nice to know that when you are putting the pedal to it, towing up a long grade, that you are not putting too much boost to your top end.
4 gauge pod available?

Boost, EGT and Trans
If your pump starts loosing pressure I would bet you would notice the loss in power

No need for a boost gauge in that truck unless your diagnosing an issue.
Fuel pressure
trans temp
egt.
those 3 will let you know what your about to kill

The gauges are 2-1/16"........only room for 3 on the A- pillar........maybe a forth atop steering column lol

That's my thoughts as well............Fuel , Trans & EGT

I was told (but don't know for sure) the loss of pressure that often KO's the lift pump can be traced back to an undersized or faulty fuel pump.

What fuel pressure are you told to look for?