Limp Mode on 1990 Daimler 4L

[Daimler 90]

Hi hope everyone's well, I'm new and have just joined, hoping someone night be able to help.

I have a a 1990 Daimler, it has just had another gearbox and torque converter put in after my last one died on me.

I have all my gears back now and can drive short distance, but more then a few miles (sometimes less) it goes into limp home mode and stays in 3rd gear.

I have checked and changes fuses, opened the gearbox ecu and checked ports. 

What else can I check as to why it keeps going into limp mode please? 

Many thanks,

Joey

[Jimbov8]

Welcome to the forum.

Ideally you would need to have the codes read to see what the car says is wrong. My money would be a wheel speed sensor.