I have a 2011 Silverado Ext Cab 5.3/A6 2WD

I installed LT Headers/Catted Y and Gears(3.73), had it tuned and made 306/327. Anyways, after approx 10k miles the trans seems to slip when shifting from 5th-6th. This only happens under load. If I 'm just cruising around town, it shifts fine. But accelerating onto the highway, between 5th and 6th the rpms jump 2k rpms then shifts. Whats the deal? the catch is, there are no engine/trans lights on the dash. I would think if it's slipping, the trans would throw a code???

Anybody have advice?

thanks

 

Needs properly tuned

 

you don't think there is something wrong with trans?

 

No, 6l80 is a badass trans but when tuned wrong they have dumb issues..when tuned correctly they hold a good bit of power

 

Yeah, ive read tons of builds where they take abunch of HP. But it just started doing it...