Your friend must be a Magician to be able to get fuel flow information from a 1987 OBD1 system? To mu knowledge, OBD1 is not capable of providing that type of information due to the computer limitations.
Besided unless you ran your rig at al speeds on a chassis dyno with the correct sensors connected, to detect a lean condition at speed or at a certain RPM range, you are only guessing.
You definately have a fuel pressure issue: But the question is: Is the fuel pressure bleeding off, or insufficient?
The early XJ's placed the fuel regulator in the fuel tank with the fuel pump. It was not until 91, when Jeep moved the regulator to the fuel rail.
If your rig is stalling at low speed but seams to run ok off idle, then you are bleeding off fuel pressure. A couple of things cause this. Worn fuel injectors, or worn regulator.
Worn injecotrs can stick and not completely close at idle, so running at idle your rig is litterally bleeding off gas pressure rather than anomizing the fuel into a fine sream. A worn regulator lowers the operating pressure to your fuel rail.
If your fuel rail has a pressure tap at the top, some of the older Renix, do not, you can install a fuel pressure gauge and take e reading. I believe it should be between about 40 PSIG at the rail, running. Don't worry if it's about 3 to 5 PSIG lower. Run your rig for about 10 minuts while observing the gauge.
Now shut you rig off and watch the gauge. The pressure should fall of slightly by a couple of punds then hold steady, if the pressure bleeds off. You have confirmation that your fuel system is at fault.
Start with the injectors, either change out the old ones for some OEM injectors that have been professionally cleanded or install a set of FORD 19# injectors as an upgrage.
But I would change out the regulator and possibly the pump anyway considering the ones from 86 to 90 were prone to failures and could leave you stranded in the trail or along the highway some day. Cheaper than calling a tow truck.
Hope this helps? See ya on the trail.