I've got a 98 4Runner SR5 4WD 3.4 AT. Several months ago I had my gear cases flushed and replaced w/all synthetic. Viscosity was correct on all. Since then, in OD at hwy speed (60-70), my tranny will downshift out of OD on hills and overpasses (I live in FL so you know we're not talking big grades). Also, when I tow (OD off of course), it will not downshift when it should going up hills (I get my hay up in SW GA so have a little steeper grades on my route). The transmission folks say there's not a tranny mechanical issue. My mechanic and I have checked the TPS, throttle cable linkage, cat, O2 sensors, MAF, trans temp sensor and everything checks out fine. Of course this new little quirk has eaten into my gas mileage as well as generally being annoying. Anyone else had a similar problem or have any other ideas?

 

I'm kind of having the same problem with my 99 4runner. Sometimes I'll go up hills and push the pedal all the way down and it will not downshift. If it helps in any way, for some reason when I pull the "gauge" fuse out it will start shifting fine. Unfortunately without that fuse none of your gauges will work including the speedometer. Possibly there's not enough power getting to it so when the gauges aren't sucking any power it gives it to the rest of the vehicle. I have no idea though. I'm still stuck on mine.