Hi all:
Latest update from my early morning run on the water. Following direction from the ESC manufacturer I removed the BEC from the esc that was supplying power to the receiver and provided a separate power supply for the receiver. Well this solved the issue and the motors ran perfectly at all speeds including at full throttle which they have never done previously. Not sure why this is the case but this has solved this issue for now.
I am still planning to upgrade my battery from a single 12 volt SLA battery to NiMH battery packs as having read up on the NiMH chemistry as compared to SLA I can see that the NiMH is a far superior choice.
Much thanks to everyone again for their help in troubleshooting this issue, it is very much appreciated.
Ted M