HELP!!! with gearbox problem

I have 92 Vogue SE classic with Autobox, and am having major problem with the gearbox. Auto gear selection fine, except after period of long motorway cruising, when back on normal roads, if I use cickdown the gearbox can't select a gear and seems to stick between gears, resulting in high reving and next to no power, also if I stop and try reselecting gears manually I loose all gears (forward and reverse). If I switch the engine off and then restart, the gearbox works fine in all gears for a while. The box has plenty of oil, having only had an oil change 500 miles ago.
Does anyone if this an electrical problem, or is it as I fear curtains for the gearbox?

Hi

Sounds like the breathers on the gearbox are shot if not the entire gearbox it's self. Take the car to an Autobox specialist and get them to check it out. The gearbox detent cable may be out of adjustment so the gearbox and accelerator cables are not functioning in sync.

Hope this helps in some way

Charlotte

Car now in garage. Problem identified as failure of pump in gearbox. New box on order with expensive bill to boot!