os x 10.10.3 installed and wifi slowed down

Had same issue. Powered down router, powered up and now all OK.

I had the same problem and tried everything listed in this thread. Nothing worked. The good news is I found a better deal with TWC, I did have 20 down and 3 up, now 30 down and 5 up and bill down $5.

I truly wish MAC could get their act together and stop sending out up dates that hurt performance. It is getting old and I don't have time to sit around and be a beta tester for them.

Time machine worked as advertised, back to 10.10.2 and wifi is back on, where it was!

Way to go MAC... I'm not happy!

Still looking good for you Ja.Bo ?

Same to me. 😟 I called apple support, they just told me to restart the computer and asked me does it faster than before. Then I said no because it didn't solve anything. They told me to do the exactly the same thing.

The App store only showed Cannot Connect to the App Store 😟

Same problem on iMac 21' (2013)

On Yosemite 10.10.2 i have no issues

Sam,

i have the exact same problem with a late 2013 iMac. I have 2 other devices running 10.10.3, but once the iMac is connected, it makes the whole network drop in and out. I had my cable provider tech here for 3 hours, and we finally figured it out. It's making one whole range of the cable signal freq drop out according to their tier2 techs.

IT doesn't matter how I connect the iMac - both wifi and ethernet kill the network.

Win8.1 in bootcamp works fine on the same machine.

i got everything I could from them and put it in a bug report to Apple.

resetting PRAM worked for me.

OS X Mavericks: Reset your computer’s PRAM

A small amount of your computer’s memory, called “parameter random-access memory” or PRAM, stores certain settings in a location that OS X can access quickly. The particular settings that are stored depend on your type of Mac and the types of devices connected to it. The settings include your designated startup disk, display resolution, speaker volume, and other information.

1. Shut down your Mac.
2. Locate the following keys on the keyboard: Option, Command (⌘), P, and R. You will need to hold these keys down simultaneously in step 4.
3. Turn on your Mac.
4. Immediately press and hold the Option-Command-P-R keys. You must press this key combination before the gray screen appears.Continue holding the keys down until your Mac restarts, and you hear the startup sound for the second time.
5. Release the keys.

Resetting PRAM may change some system settings and preferences. Use System Preferences to restore your settings.

Same with me. All iOS8 devices and a iMac running maverick work fine. My macbook air 2014 does not catch wifi save for brief period of time and of course I cannot print on network printer. Tried many of the proposed fixes in the Apple community blog, nothing worked. Very frustrating. I switched to Apple last year and start regretting it. Hope they will issue yet another update that will once and for all fix this issue. I depend on my computer for my work. BTW, Imdidn't have this wifi connection problem with OS X 10. 10. 2.

Exact same problem on 13" rMBP Late 2013, installed 10.10.3 and just my MacBook has gone from 52mbps to 3mbps. I've tried my dads old 2008 MBP which has also been updated to 10.10.3 and that is fine, my iPhone is fine too, so my WiFi connection itself is at full speed, just my rMBP is super slow on this WiFi connection.

I've not had chance yet to try it on a different WiFi connection in order to figure out if the issue is isolated to my home WiFi or not, but will do soon hopefully.

So annoyed as things were going well for my rMBP for a while now, but this has rendered it painful to use.

Guys, you can press " option (alt) + command (⌘) + R + P" immediately after you pressed power key. Keep holding on those four keys after you hear the sound of the Mac start twice. Then release those four keys, after that you MacBook Pro (air) or/and iMac will be fast as before. That worked on my MacBook Pro 13.3' retina ( Summer 2014) Hope it works on yours.

Zapping the pram didn't help my machine, nor did pulling every cache file and networking pref in the whole system.

I'be tried resetting the PRAM multiple times but that doesn't work.

However I have just booted up in 'Safe Mode' and the broadband wifi speed was full speed, soon as I rebooted back to my normal profile it was ow again so it's defo some bug lodged in my user account since this 10.10.3 update. May have to try a fresh reinstall and restore from time machine in hopes it doesn't back through.

Did you try more time on that? It didn't work on my MacBook at the once time. Also I called apple support for techonogy help. They told me to do the same thing, but it didn't fix any problem. Then I tried today, it worked at this time. If yours still didn't solve the proble, I think you have to wait for the next version to fix the bug or go to apple store.

Yes, it's a bug in this update. You can go to Apple Store to solve the problem or wait for the next version.