I apologize, both Trevor and I, among others, are intimately familiar with this particular circuit as it is unlike any other circuit on the car. We tend to get long winded and overly technical about it (especially me on the long winded part
)
Long story short the resistor's
purpose is not to change anything exactly, instead it is meant to
help prolong the life of the A solenoid. How it does this, while interesting, is not something relevant to what you're trying to figure out. As we mentioned, the A solenoid controls line pressure. However, when the resistor is not in the circuit, it has the effect of raising line pressure. This is unlikely to cause immediate damage, in fact, some remove the resistor on purpose for this reason. BUT, it is not operating as it was designed.
I want to suggest again that you have the transmission shop connect a line pressure gauge and measure line pressure at the control port and at the transfer port on the extension housing as a first step. All of the problems you are describing are symptoms of abnormal readings that would be found in these tests, and this is the first step in diagnosing your problem
FWD is not a "mode" and you should never drive the car like this unless it is absolutely necessary. If the car drives fine in AWD, leave it there.