Yesterday I discovered something about my '08 Sierra Denali that seems to really increase performance, at least from SOTP.
After runnning a bunch of 9.5 sec 1/8 mile ETs at the local track in Trailer Mode (it shifts firmer there) with the Traction Control turned off, a friend of mine suggested that I should try holding down the Traction Control button for 10 secs to disable the Stabilitrak. When I did this, I discovered that my truck shifts much higher and seems to rev cleaner with the Stabiltrak turned off. Unfortunately, this was late in the evening and the track had turned off the timers off by then, but I managed to persuade the track owner to give me a run, just to feel her out, against his flyweight autocross-modified Mazda Miata, and then gave him a proper ***-whooping. (I bet he regrets his decision now!).
Driving home from the track, I noticed that the truck now holds each gear longer and moves livelier and it will now squeal the front left wheel off the line, whereas before it couldn't even spin on a wet road!
The only problem is that I have to do this everytime I start the truck up (unless, of course, it's raining) because it resets once you shut it off.
I have no idea what the gains are HP- or ET - wise, but I swear it pulls stronger and definitely shifts higher - at like 5700 RPM- instead of 5200-5300 when i was running the 9.5's, so I think there might be a tenth or two there. I'll find out for sure next weekend and update you then.
This may already be common knowledge, so if any of you guys have tried this already, let me know if you have seen any gains.

 

Is this a stock truck or do you have a tune?

 

It's stock except for a Volant CAI. It's an AWD and I have the D20 Wheels. I tried it again last night (just nailing it on the road) and it definitely shifts about 400RPM higher @WOT with the Stabilitrak disabled. I'm about to order HP Tuners VCM Suite for it though. I can't seem to find anything that's been posted on actual ET gains from tuning the 6 speed trans, but I think there's alot left on the table with the factory tune with these trucks. since the dyno test figures that GM Performance publishes for the L92 shows the HP cuve climbing all the way up to 6000RPM, but these trucks (at least mine) shift(s) at a much lower RPM than that.

 

My shift points are at 6k and power is still climbing on the dyno chart; don't have the *****/money to go much higher than 6k.
1-2 shift is a wild ride

 

Do you disable the Stabilitrak? I guess that doesn't make a difference if you can change shifts points with the HP Tuners, though. How come you don't try making it shift higher? I would think these motors should be able to take at least 6500RPM, provided you have the right valve springs. I have friends with stock bottom-end LS1s that are turning over 7K with no issues. It appears that these motors (L92s) are still climbing the HP curve at 6000 even w/ the stock cam, so with a bigger cam, you're probably leaving a lot of performance on the table shifting at 6,000K, IMHO.

 

I was at 6700 rpm b4 the cam now it is at 7000 rpm feels like higher the rpm gets the stronger it pulls and it feels like i can get more rpm but 7000 rpm is all the ***** i have.........

 

SONOFABITCH! No wonder your truck hauls ***! and here I was thinking 5700 was a big deal! What RPM did it shift @ from the factory?
I'm thinking I'm gonna order HP Tuners now, then ARH 1 7/8" Headers and ORY with a 3.5 " electric cutout, then do the Mast cam and get Wheatley to do me an e-mail tune (since I'm overseas). These L92 trucks are the real deal for sure - where else can you get these kind of performance gains from a vehicle that I bought to tow a race car trailer to the track!

But for now, the neatest thing about this truck for me is that I just need to hold down the TC button for ten secs to get it to feel like a big Vette!

 

I sure wish I knew that you could turn off the stabilitrak that easy....that was what I hated most about my truck....

 

factory was like 6k rpm

 

You definitely got yourself a ringer from the factory man! That sumbitch truck you have there is a monster! I can only imagine what it would do with a magnacharger TVS or a little bit of spray!