I found Chrome to be evil. Chrome adds other programs to your Mac and phones home too often for my taste. I use Firefox.
If you are curious, pull down a copy of FF and go to a Google map. As you said, two fingers up and down zooms in and out but it seems relatively solid for me.
Probably in both Chrome and FF, three fingers scroll left, right, up, and down. e.g. put 3 fingers down and then move left, right, up, down and it moves the map in that direction. Is that what Scrollmaps does? From its description, you need command to zoom in and out with ScrollMaps.
You might need to toggle the "Three finger drag" setting in System Settings -> Trackpad.
I'm on 10.10.4 with a circa 2007 MPB
Hope this helps,
pedz