2008 electric club car speed sensor issue?

I haven't used my 2008 club car much since last fall but we have keep the batteries charged up all this time. The batteries are year 2014. When I used the cart this spring. I noticed it was not getting up to speed. It would start out strong then after going around 20 feet the speed would drop off and level off at very slow.

After reading some posts and talking with local dealer I determined that I needed a new speed sensor. I purchased new speed sensor and installed it. After it was installed, the golf cart ran great for around 5 - 10 minutes then the "pedal down" brakes would start to engage, then disengage, then engage, disengage and so on and so on when I had the accelerator pedal all the way down.

Also, with the new speed sensor I did the speed sensor test in the sticky (set to run, push cart, and the automatic braking safety system for "rollaway" prevention should kick in) but the automatic braking does not kick in and the cart just rolls and picks up speed.

Anyhow, could my new speed sensor be bad? Does my cart need to be "reprogrammed" or somehow tweaked to be compatible with the new speed sensor?

Also, for more info, I did not install a new magnet. The old magnet looked fine. Also, recently performed battery test by local dealer says battery's are ok. Not great but adequate. Any advice would be much appreciated.