Annoying 3790LMT

If the units have the same map version, the same avoidances selected/unselected but each is giving you a different route, I would suspect the nuvi's learning abilities are slightly different...

Nuvis supposedly learn your driving habits over usage & time. This was/is never advertised by Garmin but it's been proven in some tests I've done where hard-resetting the unit will knock the routing back into it's original algorithm.

To validate this, I would hard reset *both* units and run the same route to see if they route the same way. If they don't, I would suspect some other route-altering avoidance such as trafficTrends which tends to go overlooked and can be buried somewhat in the menus.

Is tossing it from a speeding vehicle and letting it hit the ground.

The 855 is just a plain simple GPS, no learning.
Now that you mention it, last year I had to go to the same location 3 times a week. When I was done, the 3790 predicted I would go home, told me how far and how long it would take.

A couple of buddies meet every Sunday morning for breakfast and the 3790 has shown nothing it might have learned since the 2014.10 update.

I think some people are being too picky. Not one, of any of the units I have had and or still have behave in the same manner and or learn any of my habits consistently. Map update and or software updates seems to wipe it all out. But here's the thing. Not once do any of my units take me the route I know is quicker at home. Street lights, time of day, rush hour and so on, play a huge role on which route is faster, My garmins do not care about such things. So at home I use for testing, like my 3590 not showing me traffic like my 3790 does. At home i already know how to get where i need to, don't need a GPS for that. On my trips I use it and I trust them to get me there, and they do. So it more than likely will make me take the longer Route like it will at home. Extra 10 minutes or so, don't care. I get there. I remember what it was like prior to these units. 60 million maps, momma telling me turn left at 30 miles an hour as I just pass the street. Where do we eat? Where's the nearest hotel? That's all over with now. So I really don't care that It takes me the long route. Heaven forbid they ever make a GPS that can get me somewhere in my home town faster than i can get there. Not gonna happen.

You 100%. I bought my GPS to get me from point A to point B. I know my way around my home town, don't need a GPS for that.

Can I train my Garmin to provide better estimated times of arrival (ETA)?

06/19/2012
Your device can actually learn from your driving and adapt its internal database to provide better estimates of your arrival time. The device will learn from a driver’s habits and adjust the ETA accordingly. This is done by observing what speed a driver typically drives on each speed category of road and using that data to compute ETA.

https://support.garmin.com/support/searchSupport/case.faces?caseId={c499adc0-9bb3-11dd-e87e-000000000000}

I can confirm the above using the NÜVI 255W

I don't think this adaptive reasoning works with the 2797. I drive the same route to my mother in NJ several times a month which somewhat differs from what the device tells me and so far it hasn't changed its tune.

I'm of the "if I'm driving, my GPS is on" school. So my 3790LMT gets maximum learning opportunity. The considerable majority of the time I set a destination, even when going to frequent visited and close locations.

In addition, there is a second 3790LMT in the family, but it travels with my wife. As she often just leaves it plugged into the Prius accessory socket, it turns on for a similar amount of driving, but she is far less inclined to set destinations.

OK, as to evidence of learning:

1. With the same preference settings, the two units show different ETAs going the same route to the same destination on the same map revision.
2. My subjective judgment is that my around town ETA accuracy has improved considerably during the 15 months I've been driving with the 3790LMT, and has become much more accurate than my 855 ever was for this same sort of use.
3. I go to my piano teacher's house the same way about half the weeks in the year. I prefer to take a freeway exit one earlier than the default setup suggests. After a few months my 3790LMT started suggesting that I go "my way". And not just when I accepted the "prompted habitual destination" but sometimes also when I just selected her place from the favorites list.
4. Last, yes, I do get "habitual destination" suggestion prompts. Often they are really where I want to go, although once in a while they really surprise me.

In summary, I think I observe several forms of actual learning on my 3790LMT, and in aggregate I think the learning is a net plus. I really appreciate the improvement in around-town ETAs. I cautiously attribute the continuing over-conservatism of freeway ETAs (odd, because I drive much slower than most on the freeway--but it estimates I will drive yet slower) to the fact I just have not done enough freeway driving yet.

While generally quite true, but if you are going to an address where you had never been to then you plug it into the GPS.

As an aside, the 3790 also keeps track of how much fuel I use, provided of course it is always on, no matter where and when you go!