Hi everyone!!
Try this before the SATA cable swap.
I had this issue with my bro's 13" 2011 pro model after wiping and fresh installing High Sierra on a Samsung Evo SSD. Super laggy and slow. I read elsewhere to disconnect the mentioned cables on the main chip board and a few others close by for funsies and clean the terminals. Also, disconnect the battery! I used a toothpick and blunted the tip on a hard surface to make a mini brush. Then gently move over the metal connectors on the plug and socket ends. They are relatively durable, but don't use force, just brush and look for bits or crud!
Voila, after putting it all back together the whole system worked amazingly!!
I also added new RAM, but that didn't help the sluggishness either.
crwdns2934105:0crwdne2934105:0
crwdns2934113:0crwdne2934113:0
crwdns2915270:0crwdne2915270:0
crwdns2889612:0crwdne2889612:0
0
crwdns2944067:03crwdne2944067:0
Can you give us some more details here. If you followed my instructions did you encounter any errors? If not then you likely need to do some house cleaning as well as defrag the HD.
Download this app: Disk Doctor it will cleanup the old cache & log files that build up over time. You'll also want to clean off at least 1/4 of the drive so the OS has some space. Make a good backup as well before going to the next step.
OK, once you've freed up space on your HD (the more space the better if you can). Get a good defrag tool like this one: Drive Genius.
That should do it. Otherwise you could have a hardware issue like a bad SATA cable or the HD its self may need replacing.
crwdns2934271:0crwdnd2934271:0 Dan crwdne2934271:0
Sadly a video won't help you here. You've given me enough clues to understand what your problem is!
crwdns2934271:0crwdnd2934271:0 Dan crwdne2934271:0
Your systems specs: MacBook Pro 13" 2.3 GHz i5 (Early 2011)
Your SSD's specs: Apacer Thunderbird AST680S SSD
crwdns2934271:0crwdnd2934271:0 Dan crwdne2934271:0