Any Transmission Guys? 2006 Suburban Shifting Issue

[JR3]

Up till now the trans has been shifting normally. 2006 Burb LS, 2wh drive, 5.3, Auto trans (4L60E? ). Approx. 178K miles

This started Sunday. After running around for a couple of hours we were pulling out of a parking lot, turned right and the trans downshifted to accelerate and didn't shift up WTH??. Let off the accelerator, it shifted 😕 and we continued to another store. Did the same on the final drive home.

I've driven it all week. It drives fine once in gear but I need to lift for each shift. Get the tach to 2500-3000, let up, feel it shift, resume driving.

I've read a few things. Some say VSS, TPS, trans solenoids and some say rebuild.

Some research says replace the TPS. Still no CEL light and no code present.
VSS seems to be a NO because the speedo is still operating normally.

Fluid is a tad overfull but has been like that since purchased in 2020. Probably needs changed but trying not to waste money on a fluid change if it won't help.

Any experiences?

 

[NYECOGunsmith]

Same exact symptoms my 1995 H1 Hummer with the 4L80E and 6.5 NA Diesel has had 3 times in 28 years, all three, the Throttle Position Sensor was bad, easy to replace on the H1 , takes me all of 10 minutes to install and calibrate it.

 

[Harley]

Get it scanned for transmission codes. That’ll tell you. And no, Autozone, Oreillys, etc can’t do it with their “free scan”. Transmission codes will not trip the CEL. Only a proper scanner will get them.

At that mileage and overfilled, probably time for a rebuild though.

 

[JR3]

I've read the 4L80E has issues with the TPS. Mine is the 4L60E. I'm not sure if they function the same with the same computer inputs.

I plan on replacing the TPS hopefully this weekend. The dang OE part is riveted onto the throttle body. I need to drill the rivet and replace with nuts/bolts. Hoping for the best.

I'll try to get a tech and the big scanner at the shop to see if there are any transmission codes after Christmas.

It drives just as before. I just need to lift to shift. More a PIA than anything.

 

[Harley]

A bad TPS will throw a code and a light. Would be wise to get it checked before just throwing parts at it.

Ya might luck out and find its just bad shift solenoids. They have small screens that can get clogged over time with gunk and effect shifting. They can be cleaned sometimes but at only $20 or so for new GM ones its not worth the hassle.

 

[JR3]

Get it scanned for transmission codes. That’ll tell you. And no, Autozone, Oreillys, etc can’t do it with their “free scan”. Transmission codes will not trip the CEL. Only a proper scanner will get them.

At that mileage and overfilled, probably time for a rebuild though.

Well, Scanned for codes with the big shop scanner. No transmission codes.
Only codes stored were P0172 and P0175. These are more than likely from the CAI. They have popped up prior to this situation a handful of times in colder weather and harder acceleration/deceleration
Still no CEL light.
Checked fuses. All good.
Checked Iginition and PCM voltage. Good at 14.7V. running.
ECU/ECM/PCM was replaced this year. VIN programmed with most recent updates. Replacement was a bad diagnosis from a different place for an A/C issue. A/C issue was in the high side wiring and pigtail. I still have the OE ECU and a lifetime warranty on the replacement it it turns out to be this.
Cleared all stored codes, test drove. Still has problem.

I will try to suck out the overfill this weekend. It's only about 1/2 a quart. I'm also going to go ahead and replace the TPS even though there is no code.

 

[Harley]

Check your MAF, give it a cleaning if it hasn’t been done. A dirty one can cause shift issues.

Them CAI are more of a pain in the ass than anything. Unless its piped to the outside its just sucking hot air from the engine and you’re not benefitting much if anything.

If it was me id get rid of that so called CAI and go back to the stock airbox. Thats what it was designed to run with.

 

[Maxx]

At 178k miles, just have it rebuilt and be done with it.

 

[JR3]

At this point I don't think it's a physical issue in the trans.
Still working with the electronics side. A rebuilt trans will operate the same if electrical...