Hey there, I have a 89 allante, and when my car is cold in the mornings it has been acting funny. when i start going down the road the speedometer will read normally for a second then drop to 0 mph then back up to say 35 (which is about what i am doing) then drop back to zero. as the speedometer is dropping to 0 then back to 35, the car shifts accordingly. so say i am doing 35 and its in 3rd gear, the speedo drops to 0 and the car downshifts to first, when it reads 35 again it shifts back to 3rd. it will do this for the first 5 mins of driving then the rest of the day its normal.
So my thoughts were if the speed sensor was maybe bad it could be sending wrong readings and do this. or could it be something else??? any help is greatly appreciated.