ProArduino551,
I'm the author of the guesser sketch.
I have moved forward with an improved library package that I believe is better and is much easier to use.
I would recommend using it instead - or at least giving it a try.
It is called hd44780. It is available in the IDE library manager so you can quickly install it.
It will not interfere with any other library that is installed.
You can read more about it here: GitHub - duinoWitchery/hd44780: Extensible hd44780 LCD library
There is also additional information in the wiki on the github page.
The i/o class you will use for that type of backpack is hd44780_I2Cexp.
Run the included diagnostic sketch I2CexpDiag first to test everything.
It will test the i2c signals, and the LCD module RAM to verify that the h/w and library are properly communicating.
The advantage of using the hd44780_I2Cexp i/o class from the hd44780 library is that it can auto detect everything.
This means you don't have to enter the i2c address or any of the pin mapping information in your sketch.
In your specific situation it also means means that you can swap out the LCD modules, press reset or power cycle the Arduino, and a sketch will still work without having to recompile the sketch, even when the i2c addresses or pin mappings are different.
Not only is hd44780 faster than other libraries, but it also has some extra features not available in other libraries.
Overall, it is a much better and easier to use solution than using the guesser sketch with fm's new LiquidCrystal library.
--- bill