Apologies for the extremely untimely response. I got tied up trying new things, and forgot about this thread.

So, I've tried resetting the unit with the button and it seemed like it worked in the garage. But once I took the car out on the road, the lag was back. Upon boot up, the lag isn't present, but once the nav is finished initializing (ready to navigate), the lag begins. It also isn't very good at updating my position in the status bar at the bottom. It shows the street I left the neighborhood on, but it keeps displaying that the entire way to work (it is not the same street). Trying to get into the map view is extremely difficult once the lag is going. Clicking "Accept" is not responsive at all, but it will sometimes work if you are persistent.

I've updated to the latest firmware with no change. I found a post talking about the factory service menu, and made my way into there. Initially the DRAM was listed as NG in the upper right, but after resetting to factory settings, it shows as good now. Unfortunately, nav still has issues, and I've noticed that usb music playback stutters with a pretty regular frequency (every 3-5 seconds). Bluetooth streaming rarely has this stutter, and Sirius XM and the Radio are fine (maybe the amount of processing power to stream those are dramatically less).

Playing around in the service menu, I see that nav is red, and when you go through the auto test, the tone is good, clicking next drops the faceplate down (further than I knew it could) revealing an SD card slot (with no SD) and asking me to remove the SD card. The nav test fails at this point and will go no further. I'm guessing it's the internal SD, and not this slot. Obviously I can't remove it without some disassembly, but I'm wondering if it's been corrupted. Also of note, the GPS test in that menu comes back as "passed" and shows a bunch of numbers at the bottom.

Is it possible to load the Garmin software and maps onto the a SD card, and throw it in that slot and run? Will it override the internal SD? What sort of SD card is required? I'm assuming a Class 10, is there a max size that is supported?

Thanks again, and sorry again for the late, late, late response.