Lately I have been experiencing what I believe is a shift problem cruising @ hwy speed. Briefly when @ a steady 55-65 mph speed and rpm @ 2200, I will get a sudden increase in rpm to about 3000 and feel what I believe is a shift out of overdrive. This will happen 2 or 3 times and then settle back to its normal rpm reading in high gear. It does not feel like a hard shift. I am not getting any blinking o/d light. I checked for any obdI codes any there is nothing related to transmission. This symptom seems to occur when transmission not fully warm and under slight uphill conditions. I do not experience this everyday but it has been becoming more frequent.

I have been reading previous posts and doing searches to find any similar symptoms. It seems the Turbine Speed Sensor (TSS) problems have caused a shift bang betweeen 1st and 2nd gear. I have reguarly serviced the ATF w/ synthetic. I guess I need some confirmation I am going down the correct diagnostic path. It's hard for me to believe this symptom is fuel or ignition related. I did get a memory code 639 ( Transmission Speed sensor circuit fault) 9 months ago, but I was not experiencing this problem then.

Any insight from a CD4E guru would be greatly appreciated!

1995 Mercury Mystique LS OBD1 2.5 L Duratec ATX- No modifications 70,000 Miles w/ O.E. Water Pump or Replaced: VSS, Lower speedo-cable(2X) Use: Mobil 1 5w30 and Techron Fuel Treatment.;) and Mobil 1 ATF Change every 10,000 miles