When working on my Libby, I get the impression that it was intended to be a really cheap entry level 4x4, as a way to get people to step up to their bread & butter vehicles, either the Grand Cherokee or the Wrangler. It's almost like they were taken by surprise when they realized they had produced a vehicle with this much capability, when for just a bit more they could have made it more durable and much more reliable.
A lift pump will be a huge step towards reliability, in any case.
The problem with fuel supply is not so much low pressure, but actual vacuum.
The low pressure supply pump inside the CP3 unit is greatly capable and can induce vacuum in the neighborhood of 21"hg.
This makes it easily capable of not only drawing fuel from the tank, but also (the problems of) drawing air into the system at the push-lock fittings and fuel filter head,
and also if fuel flow is restricted by a pinched line, contamination, or a sufficiently plugged filter, actual cavitation.
Both scenarios are beyond problematic, and actually self-destructive.
If enough gas bubbles are present and make it through the Cascade Overflow Valve, the compressability of this gas in the high pressure rail will cause pressure fluctuations, that will cause surging at lower rpms, as the fuel delivery maps aren't able to compensate for this variable, but still try to.
Putting the whole fuel delivery system, from the tank to the CP3, under a small amount of pressure eliminates risk of both aeration and cavitation.
It also eliminates a sizeable list of possibilities that could cause the symptoms you describe.
I also had an outside-of-tank pump that I intended to use, and ultimately chose not to, as that solution didn't eliminate the possibility of aeration, added a potential (but low) risk of problems with an added component with no proper mounting place, connecting fuel lines, electrical, etc. The in-tank solution uses all factory connectors, wires, fuel lines, adds no "out of place" component, and solves
all pre-CP3 fuel issues.
[Ediit] I don't know if the pump module from Sasquatch will have the "sending unit float arm problem" or not. I used a module from a 2006 Dodge 1-ton w/Cummins, and had to bend the float arm to work. (The float arm is spring steel and NOT easy to bend!)
To check, set the module on a flat surface, and observe the lowest 90 degree bend of the float arm.
These pictures are of a proper CRD module.
The Cummins arm comes lower, to under 1/4" from the surface it is setting on, and if not modified, due to a semi-circular ridge around the module at the bottom of the tank, will only register fuel down to about 20%, and not go clear to 'Empty'.
If your pump module has the Cummins arm, the best solution is to remove the sending unit / float / arm assembly from your old unit, and swap it into the new pump module. (one clip, slides out, 2 wires for the sending unit resistor. Either swap plugs, or swap wires. Works either way)
Dropping the tank is not difficult unless it is full. The most annoying / difficult thing for me was getting the carpet and sound-deadening material out of the way to get to the wiring.
[eidits for syntax,speling, and clarity)