I've read often about an " access panel " to the TH 400 transmission on the XJS Jaguar. Removal of passenger side carpet reveals no such panel ( Oblong or otherwise ) - - what am I missing ? Please indicate panel relative to some other feature ( e.g. shifter, seat belt clamp, etc. ) many thanks. No upshift from 1st is the overall problem - - checked kickdown switch, replaced modulator - - governor seems next.

 

The panel is on the side of the transmission tunnel, you have to get the carpet off the (USA) passenger side tunnel and the sound deadening foam. From memory it is about about level with the front of the seat. The seat may have to come out first. to get all the tunnel stuff cleared.
But quite honestly, it is probably easier to look underneath to locate it and see then what is the best way to get at it, it may be possible to do it from underneath if the exhaust pipe is out of the way, but I am not sure. The pic shows it, the rusty squarish item on the RHS

 

The governor is less likely a problem. Can of course be that the plastic gear has snapped or come loose but that is such a rare thing to happen...

 

No upshift is likely the vacuum modulator. Fist check that it has vacuum and the line is connected and then replace if that fails. It's also on the right side of the transmission.