95 Nissan Pickup sensor problem

[Tom173]

I have a 95 Nissan extended cab, 4 wheel drive, 6 cylinder engine. Problem is a fluctuating speedometer. Odometer works ok but on acceleration, I might be going 60 and the speedometer needle is hanging at 30, it will jump all of a sudden, run up to 60 or 70 and then drop back down. Anyone know what the problem might be. If it might be a speed sensor, where is this devil? Thanks