GPS screens in daylight-reflections

I presume you checked to make sure it was set on the highest brightness setting.

Other than that I have seen them with a little sun shade on them to keep the light off the screen.

They are all pretty hopeless Workhorse.

Its one of several reasons why I stick with the 276c gps which had an output of about 400 nits.

These days most only have an output of about 2-300 like most laptops.
(check set correctly as Notso said.)

New screens like Samsungs new Galaxy Amoleds will truely be sunlight readable
but for now the only thing you can do is put a cover around your unit.

The readability of these devices depends on 2 factors, the actual light emitted from the screen which competes with the external light that the screen reflects back at you.

These 2 factors need to add together to give you an effective contrast ratio of 4 to 5 or more.

So best work on mounting the unit such that it gets little light to reflect (why in dash units aren't as bad) or make up or purchase a screen cover.

P.S. Dark window tint helps as it reduces light available to be reflected back at you from the screen.

The iPad is very bright and legible. a bit bigger than 7" though.

I have found that the LCD screens of the things are polarised as well. Wearing sunglasses can make the screen dark. On mine I need to angle the screen off square to read it with the sunglasses on. Odd but one gets used to looking at the maps cockeyed!
Hope this helps.
regards, Stanley