Lay of the land: 16 loaded non-PP, 5900miles, VTA blow off valve mod, oil catch can, changed oil to Amsoil signature series (or whatever the top of the line oil is...) at 3,000miles. NOT TUNED (yet)...

When my transmission downshifts between 45-40mph there's an aggressive jerk or thud (no sound really), this happens probably between 50-75% of the time. This has been going on for over a month now. I noticed it when I got by car back from dealer for a tire air pressure sensor issue, I'm not necessarily saying it was them but that's when I first noticed it. Now, just in the past week it has done it a couple times when shifting from 1st to 2nd. This one is a lot less aggressive but noticeable and different than all the other smooth up and down shifts. It doesn't matter if it's WOT or normal acceleration or heavy acceleration, vice versa for the downshift, doesn't matter if it's coming off a WOT or just normal driving...

Any idea what this could be caused by or what the problem is?

One side of me wants to drain tranny fluid and put top of the line amsoil in it, but if that doesn't fix it and I have to take it to the dealer I don't want them to drain that oil and put different lesser quality oil back in...if I do have to take it to the dealer do I need to remove oil catch can and undo the VTA mod? Or do those not matter since they aren't related to tranny or shifting (unless I'm mistaken)?

Thanks in advance for the help here!


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Look at the receipt and see if they possibly did an update to your ECM while it was in there.  Sometimes if you're out of date sometimes they'll just do the update.

Agreed.  Possibly an update by the dealer.  Check for codes in the PCM, only the serious ones show up as CELs.  If no codes, pull the neg batt cable for 30+ minutes (to allow all modules time to go to sleep), then reconnect.  Or do a KAM reset as shown by Fordtechmakuloco
https://www.youtube.com/watch?v=hZAsoqmqhdM

See if that helps any.  Also check the tire pressures with a tire gauge to verify there are no issues on that front.  Check trans fluid level, see if it is high or low, coulda been overfilled if topped off.

Why not just bring it in?  It's under warranty.  If it happens 50% to 75% of the time, they should be able to easily see what you're talking about with a test drive.  Let them deal with it and pay for it.