FWIW my engine is bone stock!!! Not even a CAI... I replaced the original transmission with the upgraded transmission because the Lock up in 4th was starting to slip just a bit. I also anticipated swapping in a new engine But still haven't gotten around to it.

I did later get a Tune because I added a small converter and it still occasionally does it.

In my case it will go into a neutral state and I can actually rev the motor like its in neutral.

After speaking with the guy that I got my trans from he had heard of it in the past but was never able to duplicate it either. Since he is a GM Tech, While on the tech line for another job in the dealer ship he asked one of the guys if he had ever heard of this issue. He said he had, but same thing no one is ever able to duplicate it to record data or find the route cause. They both believe it could either be the valve sticking under pressure from either being loose or possibly having some type of foreign debris inside.

It's believed that the valve is getting stuck somewhere in the middle of its travel and there is no direct path for the hydraulic pressure to go. When it split's the pressure in the middle of its travel and its feeding both sides, the pressure drops to both of the clutch packs putting in a neutral state until the valve returns to one side and builds pressure again.

The only way to confirm would be to get a gauge on it and see if the pressure is physically dropping when it does this.

In my case I am rarely WOT between all gears and it is random when it happens I tried to duplicate it several times with no success. I usually don't have scan tool on me when it does happen. So for me to try and duplicate it and have a gauge on the trans pressures and logging software going is just not worth my time. Especially since its my DD.

There could be a tune issue and it's worth at least looking at but I have a feeling its in the trans.

 

When this happens is the shifter in the OD or D3 position? Obviously if something was recently changed on your vehicle then a tune should be addressed immediately before you do damage the trans trying to make it shift at WOT. Normally when I hear of this complaint the first thing we think about is the 3-4 clutch. Not sure if its hurt or not but putting a pressure gauge on the trans while this happens would help. Also verify if the command has taken place when this happens. As mentioned you can lower mph/rpm tables and also raise the rev limiter to help this condition. Another thing to consider is this. Take some time to look this article over from sonnax and see if it applies to your vehicle. http://www.sonnax.com/system/pdfs/13...pdf?1289926276

 

Good advice as always!!!

 

3 tables to mess with in the tune
Command shift MPH
Command shift RPM
Shift speed (time it should take to complete the shift)

You could also have someone look at the Force Motor Tables.

If no combination of those take care of the problem, it's in the tranny. If it's in the tranny it could be a sticky valve but it could also be excessive clearance in the 3-4 clutch pack. I like to set the 3-4 clutch pack at .015 with good clutches and good steels.

 

thanks y'all. it is hp tuners that we're using and it happens in both d3 and od. don't know about power overwhelming the clutches, this thing probably isn't much over 400hp and this trans is supposedly good to 600hp. granted, that threshold may be lowered being a heavier truck.

 

Dont get all caught up in the HP ratings advertised by companies on the internet. I have seen guys with stock hp break transmissions with 500+ hp ratings. IMO ratings are just guidelines when marketing is involved. If you are having an issue with the 3-4 clutch starting to fail this is a soft part. IMO these are things that will need to be freshened up from time to time. Depending on how you have been treating this thing it might be time to have it looked at.