So I have been one that has had transmission trouble since I purchase my focus in 2014. I love the car but hate the tranny. I have all of the latest updates and clutches in the transmission. My last repair on the clutch and TCM was October 2017. Car has been running great but in February, the transmission shudder returned. I kept waiting for it to get worse and I noticed that it seemed like it would clear up for a few days and then all of the sudden the shudder would come back. While waiting to get into the dealer, I was reading up on the forum about using techtron fuel system cleaner for the injectors. I waited until my tank was almost empty and added before I filled up. I can't explain why I did this except for the fact that I was at 74000 miles and thought it could use it. After I used about 1/4 tank of fuel the car miraculously drove perfect. But after I put the next tank of fuel in, the shudder came back after just 1/2 tank of fuel was used. While trying to figure out what was going on, I was reading more in the forum and saw where people were changing the plugs early and since the cleaner helped, I went and purchased a set of plugs. I did the plug change at 74895 miles.I drove less than 50 miles and the shudder disappeared. Now I am at 75234 and the shudder has returned. The difference though is that I am noticing an intermittent and very brief surging. I am not getting any check engine lights and the code reader is not showing any codes. The old plugs showed the engine was running lean except for cylinder #4 which had the normal blackish color. Any ideas on what could be going on? I tried searching for forum but I gave up because nothing seemed to match my search criteria.