[MrForbes]

No, my assumption here is that you are not turning too sharply.

If the wheels are connected by a chain, they will turn the same speed...doesn't matter how much weight is on each one.

Might be that you were confused by my brief wording. What I mean is that on each side of the robot, the two wheels on that side will slip about the same amount, so you can implement slip control on a "per side" basis, instead of a "per wheel" basis.

Hope this makes it more clear!