So, my AU Falcon has been going into limp mode ALOT lately and I got it diagnosed by a mechanic and the code it gave me was the P0753 A Electrical Shift Solenoid code.

I took it into a gearbox shop and they checked all solenoids and they were all working perfect.

So they replaced the Valve Body on the BTR gearbox with new oil, drove it for about 50kms and it wouldn't go into limp mode.

Not sure why this is?

A month ago when it started to casually go into Limp mode (not all the time) I replaced the oil and ever since then it started getting worse and worse.

The change of a valve body seemed to have fixed it, any one know a reason to this?

I'm kinda just posting this so if anyone else has a problem it might pop up on google and it can give them an idea on where to start.

I was charged $500 for it all. ($50 for diagnostic, $450 for gearbox valve body)

I haven't heard of this and I used to work in a Ford dealership working on the workshop counter but, it is a very common thing on the 5speed Auto in the late model couriers. It may have been that you just got a car with a wonky valve body? At least you were able to get it fixed swiftly.