Truck will not start and stay running

Can you please add some details or history, including everything you've done up to this point. What was the original symptom or problem?

Be aware by unplugging the Engine Computer, you erased its memory and that will cause other problems. Most notably, idle speed is going to be too low, often to the point the engine will crank but not run, or, if it does start, it will tend to stall at stop signs. The clue is the engine will start and run when you hold the accelerator pedal down 1/4". If that is what you find, idle speed will return to normal once the computer relearns "minimum throttle". That requires a very specific set of conditions to occur. To met those conditions, you must drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the pedals.

The biggest problem is nothing was every actually diagnosed. The Engine Computers had very few problems, so that should be at the bottom of the list of suspects. Remember that once we get this solved, idle speed is still going to be too low until you do the relearn during the first drive cycle. Until then, you'll likely need to hold the accelerator pedal down 1/4" to get the engine started and / or to keep it running.

I must point out too that Chrysler fuel pumps rarely cause running problems. Their typical failure is a failure to start up, leaving you sitting in the driveway or parking lot. A few bangs on the bottom of the gas tank often gets them going again, but the problem will act up again, either the next time you try to start the engine, or it could be months later. Once they do start up, they rarely quit while you're driving. The failure is due to worn brushes in the pump's motor. Banging on the gas tank often jars them enough for the brushes to make contact. Once that happens, the motor will keep on running.

Contrast that to GM fuel pumps. They fail in a different way. They almost always start up, then they fail while you're driving, leaving you sitting on the side of the road. Due to the way they fail, fuel pressure can drop as the pump slows down. To add to the misery, a lot of GM engines are very touchy when it comes to fuel pressure. Often an engine won't even start or run when fuel pressure is five pounds low.

Chrysler engines are much more forgiving. My '88 Grand Caravan would run fine as low as 20 psi, and would finally start to sputter at 15 psi. Normal fuel pressure is around 50 psi. The low fuel pressure occurred twice over many years on my van due to a plugged strainer inside the gas tank. That is a very elusive problem, but the symptoms you described don't really match. The biggest clue to a plugged strainer is the engine will run fine for up to 15 miles, and it runs fine when accelerating or under load. It tends to stall when the largest volume of fuel is being pumped, which is during coasting.

The next problem is the cost you were quoted for the Engine Computer. That's way more than a new one would cost through the dealer.

The place where we always start is by reading and recording the diagnostic fault codes, but that valuable information has been lost once the computer was unplugged. Since you were able to run the engine with the new computer, there is a chance it detected the problem and set a fault code already. Chrysler made reading them yourself much easier than any other manufacturer. Cycle the ignition switch from "off" to "run" three times within five seconds without cranking the engine, leave it in "run", then watch the code numbers appear in the odometer display. You can go here:

https://www.2carpros.com/trouble_codes/obd2/p0500

to see the definitions, or I can interpret them for you. It's important to understand those fault codes never say to replace a part or that one is bad. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. When a part is referenced in a fault code, it is only the cause of that code about half of the time. First we have to rule out wiring and connector terminal problems, and things like that.

Until we have a fault code to tell us where to start, I can only offer a few observations. It is unlikely a set of spark plugs would last 150,000 miles, but if they've never been replaced, start with that. It is unlikely many spark plugs would fail at the same time. When one fails, the engine will still run at normal speed but you should feel the misfire. Also, the computer will detect that misfire and set a fault code indicating which cylinder is responsible.

Since your engine is running much worse than it would with a single bad spark plug or wire, a failing sensor is a better suspect. The MAP sensor has the biggest say in fuel metering calculations. On older engines, a dry-rotted and leaking vacuum hose going to that sensor would cause way too much fuel to enter the engine, and you'd see black smoke from the tail pipe. Your MAP sensor is plugged into the side of the throttle body so there's no vacuum hose to leak, but the sensor could still be failing.

First see if any fault codes have been set, then take a look at these articles too to see if they give you more ideas to continue this discussion:

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

https://www.2carpros.com/articles/stall-at-idle