Hard Shift 1st Gear to 2nd in 2008 Tahoe

[wjoutlaw]

Just curious if anyone has some insight into an extremely hard shift from 1st to 2nd gear. It's like popping the clutch in a manual transmission like you're drag racing. My 2008 Tahoe has 113,000 miles on it. The transmission fluid was changed at 75k miles and it is a dark red color with a brown tint. It is not a black color and not looking or smelling burnt. I added a quart of Lucas Transmission Fluid to the transmission when we first got it. I am also running the Range AFM Disable Module and a stage one Jet Power Performance Module.

My In-laws gifted us the Tahoe a couple of years back when it had 89,000 miles on it. My FIL is meticulous about maintenance and it was a daily driver for my MIL who treated it very well. The motor runs nice and smooth like a dream. The Tahoe is in absolute great condition for a 10 year old vehicle otherwise.

Any insights to what the issue could be, I'm hoping for a simple fix.

Thanks!

 

[Big Mama]

How sure are you it’s the trans? Was the rear end serviced? Do you hear a thump? Describe the sound you hear with the surge. Does it always do it? When first going only? Hot out cold out?

 

[wjoutlaw]

How sure are you it’s the trans? Was the rear end serviced? Do you hear a thump? Describe the sound you hear with the surge. Does it always do it? When first going only? Hot out cold out?

The rear end is solid, serviced at 100k miles, no surge in the engine during the shift. Just a real hard shift and can see the engine RPMs drop as soon as it shifts into 2nd gear. I've experienced a rear end going out a couple of times and this is definitely not that.

It doesn't do it when the engine and drive train is cold, just when I got into the tail end of running errands after driving around town a couple of hours and everything was up to operating temperature. As soon as I got home I parked it and haven't driven it since.

The weather has been mild in the 50-60F range.

 

[PG01]

Are you sure the jet performance module didnt change your 1-2 shift? Some canned tunes change shift points or allow you to change shift points, pressures etc.

 

[thompsoj22]

can you manually shift 1st to 2nd without the harsh drop in?

 

[08HoeCD]

My humble guess is that the tune is causing the hard shift.

Can you remove/uninstall the tune to test driving without it?

 

[wjoutlaw]

I've been running the Jet Module since April of last year. I'm not sure it is the cause because it's never caused a hard shift before. I will unplug it and the Range Disable module and go for a test drive on my next day off.

 

[wjoutlaw]

Good news!

I took off the Jet Power module and ran the Tahoe an hour running errands and the shift was back to normal. So far over the last three weeks during three separate trips for errands, I got the transmission temperature up to 170 degrees and no noticeable difference in firmness of the shift either.

I have relegated the Tahoe to secondary duty as the errand runner and am now driving the Escalade as my daily driver.

After the first of the year I'm gonna drop it off at the local transmission shop and have them change the fluid and filter. It's at 119,000 miles and it is due for the transmission service anyway.

 

[Big Mama]

Great news! I wonder weeny wrong with the jet power module? Sorry to hear you’ll have to suffer driving your esky each day

 

[wjoutlaw]

I'm curious too. It just happened one day. The Tahoe isn't as much fun to drive without the module now.