My Dodge overdrive transaxle (front wheel drive) quit shifting. If I turn off the key and restart the vehicle, the transmission works again, until suddenly quits shifting again

The 604 transaxle, found in many Chrysler front wheel drive vehicles, is electronically controlled, by a computer. Since Chrysler installs the 604 in a wide variety of vehicles, with relatively few changes (aside from torque converter stall speed, and transfer gear ratio, for the various vehicles and engine sizes), to the transaxle. This can only be done because Chrysler has chosen to control the transaxle with a computer, pulsing solenoids, rather than altering pressure, to alter, as well as control, shift feel. This enables the 604 to shift properly even with varying throttle positions, engine sizes, and vehicle weights. The computer "learns", by comparing input shaft, and output shaft speeds, to determine the duration of a particular shift. They measure this comparison using a CVI value (Clutch Volume Index), which is actually a measurement of how much oil (under a fixed pressure) it takes to fully apply a particular clutch conbination. If the computer senses too high CVI value for a particular shift(which means that a clutch is slipping, for some reason), it goes into "limp mode", meaning that the computer "throws up it's hands", and quits controlling the transmission. The transmission, by design, defaults to second gear, when it recieves no input from the computer. There are other reasons, besides high CVI values, for a computer to go into "limp mode", but, regardless of the reason, limp mode commands second gear, with means no upshifts. Turning off the key, and then restarting the vehicle, resets the computer (similar to "rebooting" your computer), and the computer again controls the transmission, until it senses a shifting problem, which will, again, cause a "limp condition" to reoccur. There are relatively few problems, that will cause "limp mode", that can be fixed easily, although some things should be checked before completely condemning the transmission; consult your service manual.