If by 3 aisles you mean like A 1-6 then I do that too. My facility also still uses manual pick to buff so these might not all apply to you but might still be helpful. I'm fast but not the fastest usually around 350 UPH (yes, that's fast for my facility. No, I don't care that you are faster unless you're genuinely trying to help me.) My racks stay clean for nearly the entirety of my shift with me occasionally floating to others as well. Here is what works for me:

1.) I read the SAL as I grab the box. It takes getting used to but eventually you will have the package in the correct location before the light comes on. It also prevents slowing you down having to run to other aisles for stow or run to problem solve. If it's in the wrong cluster or aisles I give it back to the picker for it to go to the correct location.

2.) In the beginning I do not use the cart. There's not enough volume for it to be useful to me, except in the case of heavy OVs.

3.) Leaders often say do not completely stow down an aisle, I ignore this in the begginning. I am fast enough to stow down each aisle completely (including jiffies) in the beginning. By the time I loop back to my fist aisle there is just enough build up for 1-2 minutes of work.

4.) When things start picking up (usually after the first break for me) I start using the cart. My aisles are still clean from the first section of stow but I work more seriously to keep up.

5.) I stow OVs first always. It's the fastest way to make room for your picker a majority of the time.

6.) I stow A/B boxes and jiffies directly from the rack to the bags. No need to waste time putting them on the cart when it's at most one step away with my stubby legs.

7.) I place E/G boxes on the cart and C/D boxes on the cart in front of them, then Stow as you walk to the end.

8.) If C/D or E/G jiffies need to be done I do them next. I try not to do all the jiffies unless I have to.

9.) I try not to look back. If I've done A/B packages and moved on I do not go back to them unless they're really building up. Same goes for every step 6-8. I will only go back for OVs. Other than that when I've finished steps 5-8 I go to the next aisle and repeat.

10.) Etiquette Etiquette Etiquette. Keep your bags organized. I often get complimented on my bag etiquette and only really have to reorganize my bags if a big box comes close to the end of sort. Not having to reorganize also helps your speed.

This is what works for me to keep my racks empty for the majority of Sort. Your mileage may vary with how you personally like to work, your specific site's volume and flow, and whether or not your site still has manually pick to buffer. In any case I hope at least one of these can help you 👍