OK, so I'm currently converting a Lassiter Series 75 from Mafia II to TS3, but my only problem so far is that the wheels don't rotate properly, like in this thread. The Series 75 is a little longer than most vanilla vehicles, and from what I've read in the thread the only other solution is to just make the wheels a part of the body, but that's not what I actually wanted. Fresh-Prince did make a working limo, and yet I'm not sure as to how he pulled it off without any major issues.

As for the programs I'm using, I'm currently editing the vehicle via TSRW.

You might try Atavera's rig editor which is more recent than the one mentioned in the thread you linked. You could also try cloning the FP limo and looking at it in S3PE to see how it's made.

Im 99% sure you still need to use a rig editior to fix the joints.
I am currently trying to do the same and cant get it working by just using TSRW

You can now use TSRW to make new cars.
Install Atevera's rig plugin for S3PE and the S3PE plugin for TSRW
Works like a charm