Hello,

97 F150 w/ 4r70w, 90k
I was going up a steep grade, it was really snowy and icy so I turned on 4WD high and the OD off (light on) to keep it from shifting into overdrive. I was doing about 30 mph and after about 2 miles, the truck shifted into a higher gear which felt like overdrive (rpms dropped) and then the light on the stalk started blinking. It did not function normally until I stopped and restarted the truck later in the day. Do you know what could cause this?

Thanks

 

Pull the fault codes.

 

Sounds like the transmission got hot and went into "fail safe" mode, in which the transmission stays in D (3rd) for maximum cooling and the OD light blinks indicating a problem.
30mph in 4h up a steep grade was probably enough resistance to keep the transmission in 2nd gear which makes transmission hot.

 

Thanks for the replies, I will get the codes pulled and see what's up. Thanks for letting me know what might cause this as well...

 

Well, I finally had the dealership pull the fault codes and I had a B1832 Shift Motor Intermittant Fail code. They recommended a new Shift Motor. Does this seem like it would cause the transmission to downshift? I'm certain it was still in 4wd. Also, I recall this past summer I was pulling a small boat up a hill and the same thing happened in 2wd. I'm thinking the two issues are not related. What do you think?