Troubleshoot code P1494: A little.

P1494 †Leak Detection Pump Switch or Mechanical Fault

The leak detection pump puts the gas tank and emissions components under two pounds of pressure while you're driving, then a sensor watches two see if that pressure leaks down. If it does, as in when you don't tighten the gas cap, a fault code is set and the Check Engine light turns on. That fault code will indicate a small leak or a large leak. The code you have indicates that pump is not building pressure at all. Either what controls the pump has a problem or the pump isn't running. The parts guy is right; that system won't cause the car to stall, but the Check Engine light will be on so you will never know if a different problem is detected. If the pump is broken, gas will evaporate out causing emissions and reduced fuel economy. The Check Engine light is required to turn on when the detected fault could have an adverse affect on emissions.

The shaking you described is almost certainly due to misfires in the engine, not an engine mount. Some of the engine mounts can cause a single hard clunk or thump when you shift between reverse and drive, but a constant repeated shaking is due to things like old spark plugs and wires, a failed injector, (very rare on Chrysler products), or a burned valve, which is pretty rare today on all cars. For misfires, you need to start with the basics. There are some things that can cause just a few cylinders to misfire at first, but lead to stalling and letting you sit on the side of the road as they get worse. Some misfires cause unburned fuel to go into the exhaust system where it will overheat the catalytic converter and damage it. That makes a minor problem turn real expensive very fast. My recommendation is to have the misfires diagnosed and repaired right away.