Auto Gear Box Overheating and Check Engine Light

[Quinlanar]

Hi Lads
This is my first time posting. My dad and i have a 96 disco (you can see it in the profile photo) which drives grand apart from two things. Firstly the gear box. Under long driving conditions the gear box is fine for about 200 miles until we get to stop start traffic which is where the transmission fluid light comes on and if we go straight to a town the light comes on much faster. We have fitted a new oil cooler but to no avail so any suggestions to solve this would be greatly appreciated. Secondly the check engine light comes on under hard acceleration this prevents further acceleration until I lift my right foot and the plant it again. Acceleration then continues but then the light comes back this makes it hard to maintain speed and power especially off road once again any suggestions to solve this would be greatly appreciated

[Disco Mike]

When and how ofen do you service the tranny? Have you gone and had your fault codes red yet, if so what are they?
Mike