'99 Silverado extended cab Z71 4x4, 5.3L. 89k miles, K&N FIPK, bone stock otherwise and runs great.

I have a Diablosport Predator hand-held that was used on a LS1 F-Body and now used on the truck. The initial tune was their 93 octane performance tune, default settings.

The truck ran great for a few hours, then started shifting HARD, like teeth jarring hard. It's especially bad for the 1-2 shift, but still hard on 2-3 and 3-OD. The entire drivetrain cringes. Shut the truck off, start it back up, it sometimes takes five minutes of driving, other times several hours or anytime in-between to do it again.

I ran the truck through a friend of mine who's a GM Master Tech, which the driveline checked out fine. He recommended I remove the tune. I did, and installed the 87 octane tune instead. Same thing, but this time more than a day to manifest before going back into the intermittent cycle of hard shifting until you restart the truck.

At this point, I installed the stock tune back into the truck. It hasn't done it since. The tunes did not do this to the F-Body.

I called Diablo yesterday, and they were less than helpful. They're trying to blame everything but their product, although it ONLY does it with their tunes and I've had the driveline/tranny checked out. I've explained this to them and we went around in circles. They're adamant they can't be responsible, but this is seriously pissing me off, and from the symptoms, I believe it to be their product causing the issues.

Anyone have any ideas? If it is their product, how do I get them to take ownership of the fault and take care of this responsibly?

Thanks.

 

With the tune on it did not shift hard every time, just randomly?

 

It started out to shift a bit firmer and quicker, per the tune. After XXX amount of time, it would shift hard like described from that point on until the truck was shut off and restarted.

 

Sounds like it was going into limp mode, does your truck have a tranny cooler?

 

Yes, whatever factory is since it has the OEM class III tow package.

Speaking of that, the truck awhile back went into limp mode after I left the MAF unplugged and it shifted the exact same (hard as ****), although it was all the time.

That being said, when the Predator tune is in, it does not throw the SES light.

 

Im not sure, hopefully someone else can help out, but it sounds like it was going into limp mode. im not sure what caused it though

 

Yep, I tried explaining this to Diablo and they won't hear it. I'm thinking something in their tune may be interfering with my PCM, but they won't even try to help diagnose the problem.

 

Up on LS1Tech since no one here seems to be able to help?

 

Do you have a shift kit and or servo's in your truck? If not im guessing that it is most likely their tune....it would seem as if that is the only explanation

 

Nope, stock tranny.