I have a 1997 F-350 powerstroke diesel 1 ton. It has been a great truck, but I am having a problem with the transmission. It is an automatic and when it is shifted to reverse it idles faster than normal. When it is in drive the overdrive button flashes on and off on the gear shift.? It will still drive but when it shifts it is harder than normal? One of my friends mentioned a modulator switch? I have checked and added the ATF. Any advice would be appreciated. Thanks.

Ther eare two rather common causes, one external and the other internal.

You can find out for sure why the OD light is flashing by having the codes read.

There is NO modulator switch. I've never heard of that.

The external Manual Lever Position Switch (MLPS) is on the left outside of the trans, they are rather inexpensive and esay to change.

The most common problem is one of the wires inside the trans breaks or a solenoid goes bad inside the trans. This is the MOST COMMON cause for a "rebuild", and the rebuilds are most often completely unnecessary. Just replace the solenoid pack ~$200.

Thanks so much for your input. Hopefully it will be an rather inexpensive solution. Thanks again!