Larry,
The GT has narrower front sponsons and originally it had a different angle on the bottom fronts. I believe that angle has been changed back to be the same as the older G2. I really like the GT, but I run mine with the wider G2 fronts because I think it launches a little better (perhaps because they are wider and a little more buoyant?) The G2 tub is about 1/4' higher so it can accommodate a slightly bigger fuel tank however I ran my GT at Huntsville, big pond, lit it up with 2 minutes left , finished every race and never ran out of fuel.
