Help! We've also noticed a problem with the overdrive not kicking in at higher altitudes. Recently bought an '86 Toyota Dolphin & are loving it...but, when going to Death Valley a few weeks ago, the overdrive worked fine while we were in the valley floor (minus 200ft elevation) but not at all when climbing up over the mountain passes while leaving the Valley...what was the answerto your seemingly similar problem?? (without the overdrive our gas mileage is in the toilet )