OK, try to follow me here, it’s a little extensive. FYI, I have a 2004 FX4 that stay’s in 2WD while this is happening, I have the 4.10 rear end, and a Superchips tuner. This all happens between about 55-65 MPH.

I’ll be cruising and the trucks RPM’s is at about 1600. When I decide to give it some gas, just a very little bit, the truck is supposed to stay in 4<SUP>th</SUP> and accelerate just slightly while staying in 4<SUP>th</SUP> and maintaining the RPM’s around 1600-1700. Now, this only happens half of the time. The other half of the time while cruising at the mentioned speeds the truck will be at 1600 RPM’s and when I hit the gas, just slightly, it goes to 3<SUP>rd</SUP>. It actually felt like 4<SUP>th</SUP> gear was slipping until I got the feeling for the problem this afternoon. Now, I know it sounds like I hit the gas hard enough to down shift it but I didn’t. Here is the strange part. Lets say for instance that I am at 60 MPH and I hit the gas lightly and it is doing this thing when it goes to 3<SUP>rd</SUP>. If I maintain this very slight pressure on the accelerator it will shift after about 100ft shift to 4<SUP>th</SUP>. Then with a slight press of the pedal it will now act like it is supposed to staying in 4<SUP>th</SUP> and accelerating normal.
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Now I know this might have been a little confusing so let me try and sum everything up. The truck is down shifting when it’s not supposed to into 3<SUP>rd</SUP>. The only way for me to get it out of third and act properly is to maintain steady pressure on the accelerator for a little while for it to shift and stay into 4<SUP>th</SUP>, then under light pressure I can accelerate in 4<SUP>th</SUP> without this thing downshifting into 3<SUP>rd</SUP>.
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One more thing, I noticed this after I passed a big rig in my truck on a two way street. I floored it to get around him and all this started happening. On another note, when passing this truck with it floored, the shift from 2<SUP>nd</SUP> to 3<SUP>rd</SUP> was very stiff and hard due to the Superchips tuner. Much harder that I notice on a normal day to day driving or other shifts into 3<SUP>rd</SUP> at WOT. So right now I am thinking there is something wrong with the trans due to the tuner. So what do you guys think?

 

Did you modify the Transmission shift points with the tuner?

 

I left it at Superchips settings. BTW, Superchips tuner only lets you adjust shift points at WOT.

 

My truck does a similiar thing, it got to be so annoying that I lock out OD when I am not on the highway. I think it has something with the torque converter locking up, but I am not sure. BTW I have a Superchip tuner, but it behaved simiarly when stock.

 

x-star, I've read your post several times, and it's still not clear in my little mind.

You seem to be saying that your truck is downshifting to third at times when it should just unclutch the converter? Are you sure it's dropping two levels, not just one? On these trucks the normal shift goes 1-2-3-3locked-4locked. Then 4-unlocked if you give it a little throttle.

Other points, the shift pattern you are describing sounds like 'hunting' which would normally happen on a very shallow grade.

These drive by wire trucks have a few different pedal characteristics that cable trucks. A much more sensitive pedal is one.

The Superchips changes the WOT setting, which also changes the part open throttle characteristics, in proportion to the vacuum etc. perimeters the transmission receives. Thus it is possible that this relates to the shift adjustments. Easy to test, just retune with stock (non-Superchips)settings.
Chris

 

Well, I'm glad I'm not the only one having this problem but let me try and make more sense of this problem.

Chris, you said the on these trucks the normal shift goes 1-2-3-3locked-4locked. Then 4-unlocked if you give it a little throttle.

I kinda see what you are saying but from an un-technical point of view, let me tell you what is happening.

Under normal operation on my truck, lets say I'm going 60mph at 1600 RPM. If I'm in 4th gear, when I give it the slightest amount of pressure on the pedal, the truck should accelerate while remaining in 4th gear and the RPM's should begin a slow climb as I accelerate. Lets say 1700 RPM at 63mph and so on. My problem is that I am cruising at 60mph and when I hit the gas, sometimes it does what I just explained and sometimes the RPM's jump up to about 2300 RPM. When this happens, I take my foot off the gas and the RPM's go back down to 1600. Push pedal again and the RPM's jump back up to 2300. Now, in order for me to get this to stop, I gently push on the accelerator for a few moments (2300 RPM) and then I feel the shift into 4th (now 1600 RPM) and I can accelerate in this gear. Now keep in mind, this whole time my speed is practically unchanged so dont make the assumption that my speed has increased causing a normal shift into 4th.

 

It doesn't seem like you are downshifting to third. Sounds like you are unlocking the converter. Do all the usual things, check fluid level.

Be sure you are not only doing this going one direction on a certain road. If the road is a 2% grade, not measurable by eye, this is normal behavior.

Test to verify a down shift by making it rev up like you are, but suddenly hitting the OD off button, forcing it into third. At these rpms it won't hurt it a bit, you could do it all day.
If it is downshifting, nothing will happen. If it's just the converter unlocking, you will feel a sharp shift when you manual force it to third.

I am a little concerned about your TC, as there have been converter failures in a few of these trucks.
Probably nothing, but easy to test.
Chris