Thanks for your insight. In between summer travels I have been reading too many DoD funded reports from the 60s and 70s on improving water propulsion via tracks (relating to the LVTs of Vietnam I presume). The reason I see reverse going slightly faster than forward is due to the idler/sprocket placement in relation to the bow/stern pitch of the vehicle once torque runs through the driveline (there is a considerable torque reaction once the tracks are moving). I also did some further testing and without the bow fenders, at the highest speed the engine could take (about 8mph land, talk about inefficiency in the water!) I would actually go backwards instead of forwards. I think this is because there are 50% more grousers on the return side of the track than the thrust side. As with any project, more time and forethought could have developed a better vehicle with proper bow fenders, side skirting and maybe even a return chute to redirect track return current 180°. It was fun to learn about track machines and the compromises of amphibians during the build and I am glad others enjoyed it as well.
Ohh also website is up with plans/kitset available next week for those with money burning a hole in their pocket.
https://decentmfg.com/
The plans cover a revised vehicle with no walking beam, beefier axle plates, a lowered hull which provides stability in low payload conditions in the water, and a heightened/tailfinned upper hull for more freeboard. It's no Argo or Muddox, but to some it might be a fun & useful winter project.