Gemstone, one thing my husband did teaching his youngest son to drive was to find a large deserted parking lot (and snow) and practice "skidding" and correcting skids, etc. in case his son got on one.

Maybe you could do something like that with/for yourself, find a large school parking lot and "practice". If it were me, I think I'd get up at 3:00 a.m. and go out on that highway and get on and off ramps for an hour, do cloverleafs, etc.? Maybe trust a friend to do the same with you and be "another" car for you? Make it a little fun or enjoyable (go to an all-night diner for a meal afterwards and to talk about how it was for you?). If that too is still too hard maybe just gradually do more and more; think of a plan like that.

I'm glad you are taking care of yourself, going the back roads, etc. and haven't just given up going out. I'd share how difficult it is with someone(s) though and maybe ride with them on the highway, etc. and then have them ride with you and talk about it! But keeping it locked in your head and heart and thinking it is ridiculous can't help you I don't think.