1999 Jeep Laredo

Did they put it on a scanning tool? That should narrow it down to what is causing the problem. It could be many things that cause that. These are the vast array of things that it could be: clogged and broken catalytic converter, faulty MAP sensor, Faulty crank sensor(on some models), Your transmission, clogged fuel filter, bad gas from somewhere, your ECU, fuel pressure regulator, cam sensor, bad coil, and etc. Without being able to have your vehicle in front of me, it would be difficult to diagnose such a vague problem. The fuel rail itself should not be a problem bu tbad gas or dirty fuel filter, etc can cause these problems. It is better for you to make sure the people who look at it know what they are doing and diagnose it because just replacing random parts can be very costly.

Things to look at: Check the fuel pressure levels, take it to a trans shop to have it evaluated(a good one not your next door neighbor), make sure that you have spark going to your engine. If you do not know if they hooked it to a computer whiel trying to diagnose the issue, make sure someone that is knowledgeable hooks the scan tool to the computer while you start it and put it in drive and watching it stall. Hope these thing shelp, sorry I couldn't be further assistence. The scan tool should not just be a scan tool that reads codes but is also able to monitor the engine while running.