I then googled it and tried two different github versions. One being jclement.ca and another by aurock. Each time I could get both a usb GPS and also the adafruit gps working, but the lcd i2c screen? Not a chance. From what I've read there is a lot of slightly different 2x16 led i2c s.
I've since ordered another i2c and see if that makes any difference, certainly would be good if it works.