Ok, firstly don't listen to the others that say you shouldn't use ds4w for rocket league. They are incorrect.
Up until about a week ago I used steam configs, and I loved using it because I could control just about everything.
However it really does produce noticeable input lag.
I didn't believe it until I played RL for few days with ds4w and then went back to steam configs and it felt so slowwwwww.
Obviously it isn't seconds of lag difference, but I'm in my 50's and if I notice it then it must be there on my machine.
And it's not a slow PC. My PC may not be the greatest, but with a 8600k (oc'd) and 144hz monitor that I run at 240fps etc it's definitely not slow.
Add that I'm no spring chicken when it comes to reflexes should show that input lag is a problem if I notice it.
Within 2 days I noticed that I had more control over the car and ball because I had more control over the controller. It just felt more precise and definite.
I then realised that in steam configs the sensitivity of the thumbstick just felt very muddy.
It took a bit of time to get ds4w to my liking but it was worth it. I won't be going back.
And that is coming from a person who has over 1900 hours in RL. Over 200 pm KB/M set up and then used the steam configs for the next 1700 hours on 2 different controllers.
Now onwards to your issue:
Make sure you're using the ds4w program that is being worked on. I think it's by ryochan or something. All this is from memory so I could be wrong.
Anyways if you've still got problems then look in device manager/human input devices and look at game controllers and do some disabling and see what happens.
You may need to reboot after disabling.
Try to see if there is anything there that is causing issues.
Sometimes windows will see the controller as 2 different ones. One that is the physical one that works and another that is a ' redundant ghost'.
If you have one of these ghosts you want to 'find' it and disable it and see what happens.
If that's not it then maybe hiding your controller will help....
Go on to steam settings. Controller, general controller tab. If it says xbox then click hide it. See what happens.
You can also try hiding it in ds4w by gong in to settings and tick 'hide ds4'.
Reboot. See what happens.
If that doesn't help then:
Start steam.
Go in to steam settings. controller tab. General controller tab. A big pop up should happen again. Untick every configuration support in there if any are ticked. If none are ticked then tick xbox and ps options. Look to see if a controller is detected. And then untick them.
Once you've found the controller in steam click on it(I think it should say xbox, that's because ds4w is emulating it as an xbox controller) anyways click on what as been detected and hide it.
(If there is no controller then go back to device manager and enable any that you have disabled. Reboot. Try again.)
If that's not worked, then turn off the 'run on start up' option in ds4windows settings tab and then the 'hide ds4' option if you have that checked.
Basically you want your PC to think it is seeing a fresh controller.
Uninstall the (I think) vgeimbus driver from the control panel. (If you've only just installed ds4w it will be a quite recent installation).
Reboot.
Look at the controllers in devices/device manager (there should only be one. If not then find out why).
Make sure that ds4w isn't running.
Go in to steam and look for controllers again. Hide any if you see them.
Turn ds4w back on and reinstall the vgeimbus driver. Now tick the run on start up option in ds4w settings.
Tick hide ds4 in the settings.
Reboot.
See what happens.
Once you've made it so you have hidden the controller in steam AND ds4w now you need to disable the steam config that steam will use by default even if it doesn't see a controller. If you do not did this then all you are doing is using ds4w to run the default steam config.
So go in to steams big picture mode (top right of steam app is an icon with white diagonal arrows, click it). Click library.
Click rocket league.
Click controller options and choose the force off option.
Exit big picture.
Reboot or a steam restart may be needed.
now that you should only have 1 controller running and it should be running directly through ds4w. I say should because that is what it does with mine but you may have other issues with your PC.
What I'm saying is this is how I got my PC to see just one controller and run it as one controller.
If you're still having issues then I would go back in to control panel/hardware/devices and see what is in there. Then look in device manager and see what is in there.
If there are any other programs that can control the ds4 then disable put uninstall them. If you had an older version of ds4w that my be running in start up then delete them.
The above seems like it will take ages, but once you are accustomed to what I'm saying you should be able to do it quicker than it took to read it. And it is worth it.