Hunter Swan

153k 6 speed not sure of the exact model unknown if it’s been serviced, bought it used about 2 months ago fluid level is a smidge high after just checking it. I haven’t done the pill flip or the thermostat. Don’t know what the pill flip is honestly

So I went on a 12 hour drive the other day and had some really strange transmission issues arise. About 8 hours in at one of my fuel stops, when I shifted to park the gear indicator read that I was in L1 (but the truck was actually in park, had no movement and didn’t roll). Then when I got back in to drive, the gear indicator didn’t show the box around drive (and wouldn’t actually engage drive to move the truck) but oddly when I shifted to L1 the truck went in to gear and would move. Happened again about 2 hours after that. Then today I went on a quick 40 minute drive and the same thing happened when I pulled into a store to grab some food. Truck drives fine otherwise. Any idea what could be causing the issue?