I have posted before about running into a split file with Experian following a name change. This turned out to be only the beginning. TransUnion is now showing the same issue, and Equifax will be sure to follow...eventually. I wanted to provide the steps I have had to take to rectify this, should anybody else run into this ridiculous situation.
Experian
Step 1: Upload supporting documentation for your name change: marriage certificate, divorce paperwork, or court order to experian.com/upload.
Step 2: Ignore Experian's 3-5 business day disclaimer. Contact them within' 24hrs to have them escalate the submission and provide them with any additional information they are missing.
Step 3: Monitor your daily credit report for changes. If none are seen after 5 business days, contact them back to follow up.
My Experience: Experian makes numerous mistakes when merging split files. As of today, I still have two credit files. All of my accounts, history and scoring have moved to the new credit file. My hard inquiries remain on the old credit file. I wouldn't mind if they just finished things off by deleting that old file. 
TransUnion
Step 1: Contact TransUnion through their Dispute Center at (800) 916-8800. This step is important, because they have to open a ticket for the name change and split file.
Step 2: Request to speak to a supervisor in the US. The customer service representatives that initially take the call do not know what the term "split file" means.
Step 3: Snail mail a cover letter requesting the name change and merger of the split credit files. Include supporting documentation, in this case, they just want the marriage certificate, divorce paperwork, or court order. You have to mail all of this to: TransUnion LLC, PO Box 2000, Chester, PA 19016.
Step 4: Monitor your daily report for the changes. TransUnion claims to need 5-7 business days to complete the request.
My Experience: Besides speaking to multiple representatives who all told me that there is no such thing as a split file, and TransUnion not allowing faxed requests, this was not a complicated procedure. Just playing the waiting game as of now.
Equifax
Step 1: Skip the headache of a phonecall.
Step 2: Equifax requires the most documentation. You need to prepare a cover letter requesting the name change. For supporting documentation, they want: marriage certificate, divorce paperwork, or court order, copy of your social security card, copy of your drivers license or state identification, and a copy of a recent utility bill illustrating the changes.
Step 3: Fax the documentation to them. I have been told by two different Equifax representatives that the fax number changes. So, I would recommend Live Chatting them and asking for the updated fax number.
My Experience: Equifax representatives are very rude, although knowledgeable. That does not mean this request will be handled properly. I will keep you updated on the progress.
Hopefully this information can help someone else who runs into this issue. Mods, if you want this posted somewhere else, please move it. Thanks!
@Anonymous Thank you for sharing such detailed info and if that's not a headache, I dont know what is 
Experian may be the most (any explicit word you can think of) credit bureau I have had to deal with.
Update: Experian decided to keep my credit file split. All of my accounts and history were moved to my new credit file. My hard inquiries remained on my old credit file. (which is funny) So, when applying for credit or dealing with any of my creditors, I was told I have to make sure they use my new name and social in order to access the right report. I thought this was ridiculous, and tried speaking to multiple reps and supervisors, all of which confirmed this unbelievable news. Then, to add insult to injury, Experian CreditWorks tells me that they cannot update my Premium Membership to point to the new file. Instead, I have to cancel it and apply for a new account pointing to my new profile. However, whenever I try to do this, it tells me an account exists because the social matches. 
Update 2: TransUnion sent snail mail today that confirmed, they not only merged the split file, they listed both names on the report as it should be?
Update 3: Equifax is still sleeping and doesn't want to be disturbed...