The in car trip planner does take elevation into account. Very effectively, in fact.
What it does not take into account is load, wind, and outdoor temperature.
evtripplanner is useful for pre-planning, but after a couple of trips, I've stopped using and rely on the in-car systems using the following rules:
1) leave with full charge.
2) first stop of day should be last supercharger you can reach within your risk tolerance. Personally, I'm a 10 percent guy.
3) Use the energy app trip graph to track how you are doing. You can trust it!
4) At first SC stop, just charge enough to get to next supercharger plus your risk tolerance.
5) Repeat (4) for all subsequent superchargers on route, unless you want to take a long meal break... then you can charge enough to skip one while you eat.
6) If overnighting, book a hotel by a supercharger. Yes, they are not the most plush or fun places to stay, but you will leave with a full charge in the AM, and you can cycle back to (1) above.