Hello,

I have a 2015 express 2500. I've kind of noticed that when I go up a hill on the freeway or get up to speed on the freeway my engine always races up to 3100 RPM on the Tach. Then it shifts down and the rpms drop. Is this normal? does it do it on your vans too? It just seems like it's kind of a delay in shifting or something, that may or may not suppose to be there. Almost like the engine shouldn't have to work that hard to get up to 75 mph. But I don't know a whole lot about these vans so let me know if it;s NNAP(= Normal and not a problem)

My transmission is

Transmission, 6-speed automatic, heavy-duty

• TRANSMISSION AUTO 6 SPD, HMD, 6L-90

 

Likely not an issue. When you think back to the old transmissions top gear was 1:1. When OD transmissions came out the top gear was less than 1 (say .85 for 15% overdrive) to 1. The top 2 gears on the 6L90 are both overdrive, so think of 6th being over/overdrive and the fact that it doesn't go into it on a hill doesn't seem like a big deal anymore.

First gear: 4.027 to 1
Second gear: 2.364 to 1
Third gear: 1.532 to 1
Fourth gear: 1.152 to 1
Fifth gear: 0.852 to 1
Sixth gear: 0.667 to 1
Reverse: 3.064 to 1

 

Has it always done this or new behavior?
How many miles on it and when was last time trasmission serviced?

 

I am the fourth owner INCLUDING THE USED CAR dealership that had this van for 1.5 years. The service history is UNKNOWN/NA, other than that PO had the transmission FLUSHED with chemicals and a machine, and then changed the fluid and filter at 156k miles. The fluid looks pink and smells good. The dipstick DOES NOT smell burnt. The level appears to be correct but perhaps just ever so slightly overfilled. The van now has 159k miles. This behavior is not new but I've only put 1000 miles on it.

 

SHORT VERSION: after changing my filter as the previous owner had service records for TWO trans services and yet the filter was black - like 50 to 100 thousand miles black -- getting the NEW fluid level perfect or a tad over fine i reckon CHECKED at hot temp verified with scanner - and THEN doing a trans shift relearn -- which sets 6L90 shift pattern to factory -- WHILE AT 160ish degrees Fahrenheit - IMPROVED my 6L90 BIGTIME.

------------------
Bought my 2010 G2500 and the service records noted 2 fluid changes in 2 years (previous owner had concerns about the transmission)

I imagined all was OK as i got it home ok - it wasn't. -- didn't drive it for several months while i did little things to it and studied tons on youtube -- then upon going for my first real drive since bringing it home it wouldn't go past 3rd, or maybe it wouldn't go past 2nd, dunno - code said solenoid stuck open. read that it was going into limp mode. NOT GOOD.

changed the fluid - and took out the filter and it was BLACK in the oval window. I've read that even after 50,000 miles or more the material seen in the window of the filter (which the fluid gets sucked up via) should STILL be a TAN color !!!

I knew that pretty much for certain that meant the "transmission services" done TWICE by a professional garage by the previous owner were simple fluid changes - likely by just fluid pumping out via the filler tube then refilling about 5 quarts/litres. FILTER WAS NOT CHANGED !!!

When i put in the new filter (WIX) i did NOT use the crappy circular seal they give you - the new filter fit in nice and tight to the presumed OEM seal that was in there and for sure they're usually hell to get out and can cause scoring etc. and the WIX little seal was crap anyways in MY opinion.

OK, so... i used my electric pump to suck out as much as i could, pretty much emptying the pan (an awesome method) - took the pan off, cleaned it up, cleaned off the magnet too - looked at the valve body which was cool - put it back together with the re-usable gasket - and of course at this point i did the filter replacement as mentioned above.

THIS GETS INTERESTING: the van ran a ton better though for sure you wanna get the new CORRECT fluid at pretty much exactly the right level WHEN the vehicle is at FULL TEMP - like 160ish when checking the level - I check the level about 6 times as it's WAY hard to read fresh fluid i believe.

there was still some flaring and other weirds though it would go thru the gear when UP to a certain temperature - plus if i stopped after a few minutes, turned off the ignition i could get it to go into 4th and not stay in 3rd quicker.

IF you don't have a good scanner that can measure the 6L90 temperature you may run too cold or too hot. I use the android app CAR SCANNER - it's 6 bucks-ish for the pro version.
SO SO SO COOL - i have my phone on my dash and monitor tons - I NEVER drive without it.

right, so... MY van starts to shift well AFTER getting up to 100 degrees Fahrenheit --- it should get up to 160 - 165 or even 180 (180 mine never does) to burn off condensation.

HERE's the best part - when the van is at 160 if you do, or get a TRANSMISSION SHIFT RELEARN done the transmission will go back to it's factory shift pattern and start learning your driving style again - something like that.

LOOK INTO IT - don't take my word for it !-)

Anyways, after i put in a new filter and got the fluid level perfect the error went away (AMAZING) and it drove well - YET~~>> after i did the shift relearn with a GM MDI it drove WAY WAY WAY better - smooth.

coulda written the above in a better order though should be ok. basically sucked out the fluid and then saw the totally black material in the ovel shaped suck-up hole in the filter, so MY guess is that it had never been changed - causing the van to alter it's shift pattern and lots of strugglings.


NOTE: a trans shift relearn is SO awesome - the vehicle MUST be at i figure 160 F to do the relearn - it won't even do the relearn with a GM MDI without being at enough temp, like operating temp.

[BIT OF A RAMBLE - optional bit below]
I do ALL my own work now (except engine and trans internal) - learning from all the giants out there on youtube and forums - I rarely assume I've learned the best way until i really really search around as i've learned wrong a few times as well from youtube videos. Or even that there a few ways, and one of the ways is the fabulous method, or, bits from more than one video - something like that. Yep, i state the obvious, as for me it's easy to miss stuff, so i reinforce by reminding myself - hehe

 

good to know, Glad you got it working again. I am hoping that my van doesn't need this to happen. But if it does, I know what to check first. The filter. And that a relearn can be done is good to know as well.

Can you also answer my original question because you have the same transmission? you should have a good answer because yours is running smooth now, as you say.