My advice would be:
Don't let the slide get to you. If it backs up, don't think you have to keep it clean all the time. Stay at a consistent pace and you will eventually catch up.
Make maximum carries to each truck. 1000 packages at 1 package per trip is 1000 times you have to walk into that truck. 4 packages per trip and you only make 250 trips into that truck.
Space your packages. ie. 1200's closer to the beginning of section 1, 1800's closer to the end of section 1. Fill in the rest of the section appropriately. Put large or irreg packages on the floor.
When bulking out, 2000's and 4000's should be loaded closest to the truck walls, and 1000's and 3000's should line the center aisle of the truck.
The same for the remaining sections, 6000's and 8000's should be loaded closest to the truck walls, and 5000's and 7000's should line the center aisle of the truck.
I hope that helps.