As a rule of thumb, I like to deliver the 1000-4000 shelves (give or take a shelf at times) and then sort the package car. It feels like you're losing time, but you definitely make up for it having everything in order. Plus having sorted every package yourself at that point, you'll kind of know where everything is subconsciously. It sounds like you're freaking out, this sort time would also be a good time to take a breather, grab some water, eat a cliff bar, calm down.
Also, whatever shelf you're on, keep pushing
towards the front. While you're searching for packages on a shelf, organize that shelf at the same time. If I'm looking for something on the 1000 shelf and I don't find it and it's not on the floor, I'll search about 1/3 into the 5000 shelf. If you're searching for something that's a pick up stop or very close by, you can afford to not spend as much time looking. If it's a stop that's towards the edge of your route that you won't be nearby later, you may want to give that stop more time to find the package.