OK so after a few weeks going back and forth with TV Nav where I bought the unit and Garmin, we finally got it all straight. The 378 comes with a combined CN NT and US Inland Lakes map DB. Becuse of this, there is no way you can load PC created routing to the unit. All manual routing must be done on the unit itself. I'm sure most of you can appreciate the difficlty in doing this. Myself, I have a lot of route files, and I like to DL other peoples files as well. These are all totally useless with this unit. Now the 478 does not combine CN NT with the salt water blue charts. Therefore you can load PC created routes to the unit. Luckily, TVNav is helping me out. They along with Garmin have agreed to exchange my unit for a 478. I can't say enough good things about Darrell at TVNav and their customer service. You can bet I'll continue to buy from them in the future.