@Duke4221c A LOT OF LITHIUM GREASE!
To add onto this, several teams revealed custom linear sliders that are miles ahead of the ones vex uses. However, if you're not feeling this route, lithium grease is a common way to solve this, you should also make sure your slide trucks are aligned with the slider bar itself. Another way you can reduce friction is to file down the trucks maybe 1/16 or 1/32 of an inch, or however much you can without making it leave the bar. This results in much less friction, with more wobble in the slider bar. Something else you can do is to make sure your trucks are as close and as sturdily mounted as possible.
Another thing to do is to use bearing blocks everywhere. Without bearing blocks it'll sound horrid, however, I don't think this is an issue you have. Something else you can do is to use shoulder bolts, as they reduce friction from metal on metal, and keep spacing incredibly tight. Good luck with the rest of your season.
Edit: These are trucks btw: insert, and outside slider