Bill WB8ELK used one from these guys http://www.inventeksys.com/html/gps_modules.html
The unit as shipped from the factory doesn't do high altitude, but they do provide alternate firmware that can be loaded to do high altitude. I'm sure Bill will share the details; let me know if you need his contact info. If you're buying quantity, they may even be willing to do an order with it preloaded. Of course, the GPS18 still works great... -Jason kg4wsv
