I've given it another run. It is just as fast forward or reverse except it wheelies in reverse.
I guess it's just grip with my tyres or how it has no stearing in reverse at the front. My batteries are poor quality, I'm sending them back, well... getting rid of them anyway and buying some proper ones.
If it's just a matter of wheelies, that could be a couple of things. Weight distribution of the truck, and maybe some of the power control settings on the ESC.