I have 2 Jeeps, both are AMC 360 engines w/ 16197427 TBI systems.

#1-('88 Grand Wagoneer) I have a stock chevy truck in tank fuel pump installed in the tank & 3/8" supply line / 5/16" return line.
FP is ~13psi and the truck has been running very well for a few years now.
It was originally a 1227747 that I re-pinned the harness and swapped to the 16197427.

#2-('90 Grand Wagoneer) has been a real PITA, lots of issues.
Every time I find an issue and fix that something else seems to pop up.
(Exhaust leak, vacuum leak, different throttle body, new injectors, IAC)
Also started w/ a 1227747, but swapped over to a 16197427 because I had one, and I like them better.

This one the fuel lines are the stock Jeep sizes 5/16" supply and 1/4" return.
Fuel pump is an Airtex# 2182 mounted to the frame rail.
FP is ~15psi right now, and the truck runs well, but seems like the fuel system is inadequate?
@13psi the VE tables were getting maxed out.
I have monitored fuel pressure while driving w/ 2 different gauges and the pressure is steady.
I have monitored the fuel pump voltage while driving, and it's battery voltage ~14.2 and never decreases.
AFAIK the engine is stock, but for 177k it has great compression and will spin the tires easier than my other one so ?

So back to my original question, can you have adequate constant fuel pressure and still have a volume/delivery issue?
Could the smaller lines be an issue?
I've read several places that the small lines work just fine, but I'm wondering why 2 virtually identical vehicles have such different VE.