'04 Grand Cherokee mass amount of engine codes!

Those codes are pretty basic in their meaning but I can't imagine any cause they could have in common. Were you disconnecting things in an effort to identify the problem?

Code 122 is low voltage from the throttle position sensor. When the sensor is disconnected, the voltage will get "pulled" to either less than 0.5 volts or higher than 4.5 volts to force it to set a code. Yours may get pulled down to set a code when it is disconnected while the ignition switch is turned on.

1490 and 1489 have to do with the low and high speed radiator fan relays. Unplugging them will set a code.

300 means random cylinders were misfiring. 301 means cylinder 1 was misfiring. 305 is for cylinder 5 and 306 is for cylinder 6. It doesn't matter if those misfires were caused by bad gas, disconnecting a coil, a bad spark plug, or a vacuum leak, the computer detects the slowdown in the rotational speed of the crankshaft, not the cause.

455 is a large leak in the fuel supply system. That is almost always from removing the fuel cap while the ignition switch is on.

It's also possible some of these codes set earlier and are adding confusion. The best course of action is to use a scanner to erase all of the codes, then drive the vehicle to see which ones come back. I don't recommend this but codes can also be erased by disconnecting the battery for half a minute. Doing that WILL result in a huge repair bill for Volkswagens and some GM products. On most Chrysler products the engine will idle too low until you drive them and the computer relearns "minimum throttle", but that is one way to erase codes. If an intermittent problem, or one you caused, doesn't come back, it will erase automatically after about 50 engine starts.

I can't think of any individual failure that would set all of those codes at the same time.