odd stumble when accelerating

[RLC2020]

I've owned my 2015 Yukon for about a month now and after about 1200 miles I've had a nagging issue with it that I'm hoping to get some suggestions with before I start replacing stuff.

This only happens in the morning on my first drive with it and only happens under certain throttle positions.

The truck will start right up and run fine, it does fine under light acceleration leaving my driveway and driving down my backroads. When I go to pull out onto the very busy main road in town I have to use moderate acceleration, this is where the issue occurs. After the shift into 2nd gear and sometimes after the 3rd gear shift, the engine will fall flat on its face and it will act like it has no power. I have to give it about 80% throttle for it to "snap out of it" and start pulling again. I've tried giving it full throttle and it runs through the gears just fine, it's only at mid/moderate throttle that it happens. The weird thing is that it's fine at idle (other than a slight rough idle sometimes in gear with the ac on) and it's fine through 1st gear every single time, it's when it shifts to second/third that the issue shows up.

So far, I've done an intake cleaning with seafoam and dumped a can in the gas tank as well. Did not make a bit of difference. The air filter is new and the oil is clean and full.

Any suggestions? I'll try to get a video of it tomorrow on my way to work in the morning.

specs are down below

 

[Fless]

Have you put a graphing scanner on it and graphed the TPS over its travel? Throttle body clean? MAF clean?

 

[swathdiver]

Have you put a graphing scanner on it and graphed the TPS over its travel? Throttle body clean? MAF clean?

Good thinking about the flat spot on the TPS! I had that once before on a Buick way back when. I'd also be looking at fuel pressure.

 

[Doubeleive]

needs a tune, @BlackBearPerf the k2xx shift like crap without one

 

[OR VietVet]

"D", all the above.

 

[RLC2020]

Thanks for the responses so far. I did clean the throttle body and the MAF, forgot to mention that. They were both very clean, but I hit them anyway while I was in there doing the seafoam. I was assuming it wasn't a software issue as it only seems to do it when it's cold. Once it warms up it goes away. However, I will look into the tps as well. That part can be had for $50, worth just replacing it to see if that's the issue? I have no idea how to graph it, I have a basic OBII scanner. I'll purchase something aftermarket if it makes sense to. What do you guys recommend for that?

Thanks

 

[Fless]

Some of the phone/tablet apps can graph these, if you have an OBD dongle that transmits to the phone/tablet. I use TorquePro, $5 in Google Play with a OBDLinkMX+ Bluetooth dongle. I haven't looked to see if the app will graph that particular PID, but it does a good job of graphing others.

Other folks may have suggestions.

 

[STORMIN08]

try driving in tow/haul, the increase in shift pressure can replicate what a slightly better tune can do...see if that helps or changes.

i have my trans tuned to shift at 150 rpm higher 1-4, it is night and day better.

 

[BlackBearPerf]

needs a tune, @BlackBearPerf the k2xx shift like crap without one

Right on, we would be happy to help!

 

[RLC2020]

I'll try tow mode and see if that makes a difference. I disconnected the battery the other day to "reset" things. Seems to have made it worse. It was actually shifting bad in all gears for the first few miles I drove it after that. Now it's back to just doing the 2nd gear stumble, but it's worse. I almost got rear ended the other day, it stumbled and I had to floor it to get it to accelerate while merging. Really not sure if this is a trans issue or a tune up issue, but the engine seems to run fine everywhere else. I have 55k on it and no record that the trans fluid was ever changed. I'm contemplating doing a fluid / filter swap first to see if that makes any difference. I'm nervous to "tune" anything right now because if I have a real issue going on I don't want to cover it up or make it worse. I'm kinda lost right now as to what to do first. I'll try to get a good video of it asap