I have a '96 FZJ 80 that has trouble going into overdrive when it's cold. I run the truck for about 1 min before I start driving and it doesn't shift into overdrive until around 2 mi. or so depending on how cold it is (40 deg. down to 0 so far). It did not do this last year. Fluids were serviced by stealer in the summer (for the last time). Any suggestions?