Sorry if this has been addressed but I searched and could not find exactly what I was looking for.

When I am driving the truck, let’s say im going 40-50 in overdrive. When I slowly step on the gas to accelerate the truck will have this huge CLUNK when it is trying to shift down from OD. It feels like the damn tranny is about to fall out of the truck! Now I know it is time for a tune up because it is starting to miss just a bit as I can feel it when I punch it, it doesn’t accelerate like it used too. But this clunk has me worried, if I immediately let off the gas and then get back on, it will downshift correctly and accelerate. But if I ease on the gas it will CLUNK every time!
Anyone else have this problem or know what the issue is? It used to have the drive shaft clunk when I would start and stop but when I Teflon greased the yolk that went away, is this some extension of that same problem maybe?

 

It could simply be a misfire - get those plugs changed.

 

Start simple. Has your battery been disconnected lately? The adaptive learning for the ecu can be screwy sometimes. if you have not disconnected your battery lately then disconnect the negative cable and positive cable then touch the two together. This will reset your ecu. reconnect and Take it for a drive and see what happens.

 

I started having the exact same problem recently. Have been looking for a good answer on here...

 

Mine does this too. I looked and found something called a low-grade misfire and that seems a likely culprit. If I switch off the OD, I don't have any knocks of sputtering. Plugs have about 50k. Changed fuel filter already with no change. No codes thrown either....

 

Does this apply to me if I have a tune on my truck or do I need to return it to stock before I do this?

 

I had that exact problem you describe and I did new plugs a month or so ago. Hasn't done it since. That on my 08 5.4 4wd.

 

Also check your transmission to cross member mount. I have had the two nuts work themselves loose and that trans jumps all over the place

 

Might as well return to stock tune. This way you eliminate to potential issues.

 

My truck does the same thing but on every downshift but upshifting I fine. If I put o/d off it shifts fine down and up. Would the plugs be a possible problem for me as we'll? It did it coming to a light once and after that it does it everytime. Did u figure out your problem?