Fuel pressure is very important and must be within specifications! If it is too high or too low it can cause drivabilty problems. I would definitely find out the specs!

Also was the fuel pressure regulator replaced along with the intake?

And sounds like its running too rich with the black smoke out the tail pipe. U could have a bad oxygen sensor! The heated oxygen sensor is very important to control not only the cars emissions but it also helps the vehicles performance! If it is not working properly it can result in a number of problems like rough running stalling hesitating bucking and jerking. But more common than that if it is lazy, the cars gas mileage can drop considerably, and sometimes not even set a check engine light on the dash!
The fuel control Heated Oxygen Sensor (HO2S 1) is mounted in the exhaust manifold where it can monitor the oxygen content of the exhaust gas stream. The oxygen present in the exhaust gas reacts with the sensor to produce a voltage output. This voltage should constantly fluctuate from approximately 100 mV (high oxygen content - lean mixture) to 900 mV (low oxygen content - rich mixture). The heated oxygen sensor voltage can be monitored with a scan tool. By monitoring the voltage output of the oxygen sensor, the PCM calculates what fuel mixture command to give to the injectors.

Be sure there is no oil or coolant burning in the cylinders as this could cause misfires as well!

Just some ideas.