99 F150 King Cab...188K now...Have had it since 08 and 78K....Anyway, @ about 115K I remember having it in cruise control on highway and was at 'just' the speed where it kicked in and out REAL quick for a few seconds and I thought WTF?????...Let off the gas and it was ok...Did it again, IN cruise control later, but when slips my mind...Have NOT used cruise control since, but...Now and then through the years, the truck would shudder when shifting at around 55-60+/_....No big deal and lived with it...Well, now and then is getting short and frequent....Usually shuddering at about 55-60 but can and will at almost any speed...Does seem to do it if the RPM's are around 1300/1400 more than 1800 etc...But, it does it more than I like so...Thinking Torque Converter but NOT ruling out trans??...Whats the general consensus on this....

 

Well, my first question to you is, when was your last tune up, and if recent, what brand plugs did you use? What you are explaining sounds like it could be a low grade misfire that just hasn't hit the threshold to throw a code.

 

Asked my mechanic a few months ago if I needed plugs etc...Been about 60K since...He said not 'really' needed...The shuddering was before and after tune-up, but more frequent now...

 

Did you/he use Motorcraft plugs? If not, I'd give those a whirl and see if it goes away. Autolites, Bosch, Champion.... all of those do not do well in these trucks.

 

I don't have a lot of experience with automatics but I did once have to replace a torque convertor for exactly what you describe. Low fluid maybe. Have you noticed any trans leaking in the driveway or on the transmission?

 

No...Don't see any leaks or evidence of any....I'll add that even when it shifts 'good' sometimes it seems like it 'clunks' like u-joints or the like...Sometimes even harder...Just drove it about 50mi and a few little clunks but no shuddering, BUT, I know when to keep on the gas to minimize it...





As far as plugs etc, I'm no mechanic and it runs FINE except when it shifts??..Taking it to my mechanic tomorrow for a look-see...

 

Change the fluid/filter then you can add some lubeguard if it's still a problem, it just might work.
Sometimes the trans is just too far gone to save.

 

i wonder if the issue isnt with the cruise control?

 

Cruise control with a low grade misfire will exacerbate this, especially in the 3-4 shift.

 

Could be a simple transmission filter I have a 1999.Jeep wrangler I use to plow my .65 mile drive and change the transmission and transmission filter every other year.

PS I own a 2019 ranger and 2020 f-150