Sluggish Dragging Zetec Feeling

[Jeff]

Hi.

I just purchased a 2002 reg Focus Zetec with 44k on the clock.

Sometimes when driving along if i take my foot completely off the gas ( still in gear)

the car starts to slow instantly like i am pulling a caravan up hill or the hand brake is on.

It does not feel like or happen all the time. ( This is not with AC on either)

Could this sluggish drag be to do with the Gearbox Speed Sensor ?

The speedo works fine but sometimes revs hang before falling.

All help appreciated

Jeff