Typically if you are having issues traveling in one direction a fix would be to calibrate the directional pot and switches, but you need a curtis handset to be able to do this. Crown will have this handset.

I tend to try never to rule out batteries without testing them even if they are brand new. Recently there has been a large ammount of batteries that die a few months after installation no matter the brand. I'm not sure why the quality recenty dropped off the last few years but I have had to complete a lot more warranty claims over the last 2 years.
From my memory I think costco batteries are rebranded Interstate Batteries, which are not my favorite battery brand.

Best of luck, let me know if you have any questions. I work on alot of these pallet jacks.