No power to Transmission Control Module

Hi all, just looking for some advice as I don't work on cars often at all;

I've taken my automatic 2005 Focus LX 1.6 in for a diagnostic test as it's stuck in limp mode, I've been told there's a problem with the transmission control module, it's not showing up at all on the diagnostic results and the gearbox isn't working right as it jerks violently when shifting into D and R, barely accelerates beyond 3500rpm and seems to be stuck in 3rd or 4th gear as it rolls of the line painfully slow.

Basically I'm looking to replace it myself as the internet's told me replacing it at a shop would cost £600-800 (not sure how accurate that is). I know on the 4-speed auto that the TCM is located on the bulkhead on the N/S but I can't seem to find just where abouts where that is.

Generally wondering if anybody has had this issue before and knows of anything to try? And also wondering if anybody has dealt with the TCM before and could advise me on where it is/whether it's worth tackling myself with little experience.

Cheers