2011 Silverado 5.3 shifting weird

Bailey mays · March 25, 2015

I have a 2011 z71 on 35 inch tires and ever since I have got it it kinda feels sluggish and like it downshifts weird like when I'm stopping it will down shift and i can really feel it like almost jolting me forward it is very annoying and the whole motor itself feels sort of sluggish idk if it's just something to do with my tires or what this is any suggestions or anyone else have similar problems? In a way it feels like it's bad fuel but i wouldn't think that is the issue.

Doug_Scott · March 25, 2015

Your tires are about 4 inches larger in diameter than stock. That will make your speedo off by about -12%. That means when the speedo says you are going 60mph, you are actually going closer to 70mph. This is assuming no one has changed the pcm/tcm to correct speedo.

Putting larger diameter tires on has a similar effect to changing the gears in the differentials. Your truck likely has 3.42 gears in it, swapping to 35 inch tires makes it fell like you have closer to 3.08 gears. If you have a buddy with a 07-13 Chev or GMC pickup with stock wheels and tires, see if you can borrow his wheels and tires for an hour. Does your truck have a body or suspension lift kit?

Bailey mays · March 26, 2015

Suspension 6 inch and my speedo is re programmed so it is correct and it does have 3:42. It feels similar to like if I were to put it in manual mode and down shift it fast like the Rpms shoot up faster and kinda jolts me forward when I'm on the breaks. And when I'm taking off at a stop it feels sluggish as if it is running out of gas when it isn't. It hasn't always been like this it's getting worse as time goes on but it seems to kinda have a temporary fix when I put in fuel system cleaner but barely much difference im not sure what it is

Bailey mays · March 26, 2015

Maybe it's something to do with the switching back and forth from 4 and 8 cylinders? Anyone know more about this?

Doug_Scott · March 26, 2015

Suspension 6 inch and my speedo is re programmed so it is correct and it does have 3:42. It feels similar to like if I were to put it in manual mode and down shift it fast like the Rpms shoot up faster and kinda jolts me forward when I'm on the breaks. And when I'm taking off at a stop it feels sluggish as if it is running out of gas when it isn't. It hasn't always been like this it's getting worse as time goes on but it seems to kinda have a temporary fix when I put in fuel system cleaner but barely much difference im not sure what it is

There is something that you may be experiencing at slow speeds. When the truck nears being stopped, the transmission downshifts to 1st. When you put the transmission in 1st manually with gear shift(or button), that enables engine braking, so when driving in manual 1st, the engine rpm follows truck speed. When the transmission downshifts to 1st automatically it does not engage engine braking. The net effect of this is that once the transmission does this, the engine will return to idle if your foot is off the gas pedal. If the truck is not stopped, and you step on the gas, the engine will rpm will jump up to where it would be if you had never removed your foot from the gas pedal. My truck does this when I turn on to my street, unless I approach the corner slower and do not lift off the gas. In my case it did not do this pre-tune. I would rather put up with this than put up with the stock trans tune though.