Shifting funny. 1st to 2nd

[Didgeridoo86]

This is my first post. Thank you all so much in advance.

I have a 2003 GMC Yukon Denali sport with the full tow package. 6.0L
143,000k.
OK so I have no transmission error codes. I did have a p0300 code.

So from a full stop accelerating it goes through fist gear perfectly and about when it should shift into second the revs drop off and the throttle stops working. If I take my foot off the throttle for about 2 seconds it will go into second and it's fine through the rest of the gears. Like I said there are no transmission faults on the diagnostic read out so I am really scratching my head on this one.
Trans fluid levels are good and the fluid color is good.

I had some fuel tank leak codes that I tracked down to a vent hose that was disconnected. p0452 and p0456. That might also be 02 sensor and I heard the transmission shares that fuse, is that right?

 

[Chevy_Lover31]

I think I'm having the same problem too, I have an 06 Chevy Tahoe, 154k on it, I think it's with my second gear, cause it goes into 1st gear but when it changing to 2nd gear the revs drops off between (25-30 mph is when the revs drops off) but when I speed up to 35 & on it sound clear, also I haven't got any warning lights I'm so puzzled & my mechanic is too...


ChevyLover

 

[Didgeridoo86]

Yeah my case is a bit different. It only happens for me at about 10 to 15mph and when it does I can hear a weird buzzing/grumbling sound coming from under my left foot. It doesn't feel like it's gears or transmission. It seems like the sound comes from the driver side tire. I know it's not though. The power drops off and it makes that sound for about 4 seconds and then the power smoothly comes rushing back in. There is zero clunking or jerking. Just a whoosh of power and the truck takes off.

 

[Chevy_Lover31]

I think I'm having the same problem too, I have an 06 Chevy Tahoe, 154k on it, I think it's with my second gear, cause it goes into 1st gear but when it changing to 2nd gear the revs drops off between (25-30 mph is when the revs drops off) but when I speed up to 35 & on it sound clear, also I haven't got any warning lights I'm so puzzled & my mechanic is too...


ChevyLover

Here's a update my problem was fixed it was something going on with my 4wd auto switch


ChevyLover