I think your issue, simply put, is due to the weight-to-horsepower ratio of your boat. The G-Series is a great boat, loaded with standard features. The addition of the Sea Legs and extra battery is the equivalent of carrying 3-4 extra passengers.
My 22 footer with 2 logs and a black 115 ran 27-28 (gps). I added an express tune and fiddled with the transom height. My top speed was... wait for it... 27-28 (gps). Much better handling, but top speed never budged.
Expecting more from that heavy of a boat and a 115 (of any color) is a pipe...
I don't think your boat/trailer combo is as heavy as you describe, but fuel, water and gear does add up fast. I think 5K# is a maximum figure. Do heed the ramp advice from the reply above. Know your ramps... spring, summer AND fall.
If you boat with children, you will be able to relate to our adventure and boating with young children is ALWAYS an adventure. Spending the day on the water while juggling naps, meals, potty stops (or those dreaded swim diapers) and meltdowns are usually part of the deal. Plus, there is that...
Always best to perform a search prior to posting. This topic has been discussed frequently here, including a thread in the past month or so. I'll leave this here for a couple of days so that you see Jack's link above, but then I am going to hide it as there is no need for redundancy.