Thanks! Now I know what it is. I recall there was a program that imported a higher resolution into TS2018. I never it needed because the DEMs I used where already higher resolution.
Another difference between the two sims is the night lighting. I'm still waiting for the Trainz crew to come up with a better way to deal with night lighting and how light shine is rendered on other objects.
It was called Redem. I still have a working copy but the author stopped selling a while ago.
Unfortunately DTG never fixed the bug where anything other than low res DEM crashes the editor at latitude lines if you use the built in importer.