rweber95 - I tried your method. Here are my procedures and my results.
I opened for edit all the built in assets from 2006.
I then imported them to TC.
I then reverted all of them in 2006 back to their original state.
I then opened for edit my local assets from 2006 and imported them to TC, just as I did the built in assets.
I then reverted all the locals back to 2006.
So far, so good!
I then opened for edit, 4 routes and all their dependencies, and imported these to TC. Then reverted these back.
I did the same for all the sessions for the 4 routes - same procedures.
All went well. A few hiccups but no problems.
A cursory look over my routes was promising. All looked good.
Then the fun started. When running my sessions in Driver, I had variations of all the following:
Locos with no cars.
Locos with just a few cars.
No locos. Some cars.
18 Well cars, double stacked, that showed up in Driver as 4 plain vanilla flat cars with no loads. I gave this one the blue ribbon for the best screw-up!
Conclusion is: TC is much too fussy about everything being "politically correct" that for me it's not worth the effort. It seems that TC can find something to fuss about with almost every asset. If one wants to move a route or two over to TC and start a few sessions from scratch, with only "non faulty" assets, perhaps it would be worth the effort. But for me, it simply isn't worth it.
I deleted TC once again (I think this is the 4th time). There just isn't anything there that appeals to me. I'm not into trolleys, trams or whatever they're called, and the routes are - really - well - you fill in the blank.
rweber95 - your method worked fine. It's just that TC didn't care much for it.