TB42 Auto 4th & O/D

Hi there fellow PAT/SAF enthusiasts

I need a diagnosis please, I have a 1992 Safari TB42 efi with 200k on the clock.

My issue is while cruising and reaching 100-110 kph the auto will grab over drive, but as soon as i feather the accelerator to maintain the speed im comfortable with the revs go from overdrive 1900rpm to 2600rpm and will chop up and down whilst trying to maintain this speed on flat road, if im in over drive and lift my foot a ants dick it shoots up to 2600rpm and looses speed, i then put my boot into it and instead of staying in 4th and picking up speed it engages overdrive again, is there a vacuum line around the wrong way or something because it seems backwards to me.

TIA:animierte-smil

Really should have done an intro first mate but try a torque converter lock up switch mod , use the search function top right corner to see what others have done .
Might even find you're problem and how to fix .