1994 Other Nissan Models Gearbox

I have a 2 ltr Nissan Primera with 4 speed auto box and electric overdrive M reg (1994?).

Recently while driving the engine suddenly over revved and lost power, similar to what happens in a manual box when the clutch goes.

In D (drive) it will go from 1st to 2nd, but just as it is about to jump into 3rd it revs but there is no power.
There are no warning lights, no indications of any other fault, it makes no difference if the overdrive is on or off and the TF fluid is fine . It will drive in reverse and I can drive around in 2 (2nd) at 30 mph with no problems (except it drinks fuel of course.)

Does this sound like a major fault or is it something simple given that the car will driving normally except for the problem of not dropping into high gear.