03 GMC 2500HD Allison 1000 issues

8Point1 · July 22, 2017

Truck is a 2003 GMC Sierra 2500HD.
Allison 1000 trans, 8.1L Engine.

Truck has 93k miles on it.

Problem started about 2 or 3 months ago.
Between 2-3 and 3-4 shifts, there would be a hesitation in the shift.
Almost like it would go into neutral before it shifted.
When it would shift... It would shift hard.
Seems to only do it after driving for several miles, trans temp gauge will be close to 200 when it starts acting up.

Immediately started asking around for a shop that was some what local that worked on Allison transmissions.

A good friend of mine recommended a shop about 50 minutes south. He claimed this guy/shop rebuilt his allison trans in the same make/model truck and it can supposedly hold 1000hp.
So im like alright, cool... Found a guy/shop who services allison transmissions.

I called the guy, i dropped the truck off that night or the next night.
A few days goes by, he tells me he cant get it to act up. I told him to turn it into his daily driver, drive it home, drive it to lunch, drive it around town. It'll act up.

He calls me back 2 days later, he got it to act up. He claims that my MAF sensor is bad and its causing the trans to receive false readings on when to shift or some shit and that it has caused my trans to slip. He claims my trans needs rebuild or replaced.
I gave the guy $3800 and some change for a reman allison trans with a matching converter. He also replaced my MAF with an OEM replacement and also fixed my oil sending unit.

I get the truck back, put 400 miles on it and it starts doing the exact same thing. Shifting horribly.
I call him within 10 minutes of it happening, i take the truck back.
He has it for a week, claims there isnt a thing wrong with the trans.
Says he cleaned up all of my chassis grounds, all of my electrical connections related to the engine and the trans, he also claimed that he added an additional ground somewhere, cant remember where.
He drives it for 2 days after to make sure its good. He calls me on a friday, which would of been last friday. Says its done, i parked it outside, hid the keys come get it its ready.
I drive down friday night and pick it up.

2 days ago i drove it about 200 miles, started doing the exact same shit!

After the 2nd occurance, i realized that i did not need to spent $3k+ on a reman transmission.

I just dont know what the hell to do at this point.
Ive never had something like this happen, spent a bunch of money at a legit shop and then turn around and have the same issue on mulitple occurrences now.

Input?
Heard of an issue like this before?

casey.mikl · July 22, 2017

Does the transmission look clean? If it's a reman unit, the housing should be clean as if it was a new trans. If it's dirty and looks as if it's never been out, chances are the guy didn't switch the trans at all and just bandaided the issue.

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8Point1 · July 23, 2017

oh he for sure swapped the trans out with a reman.

Im not questioning that... one bit.

KansasGM · July 24, 2017

The company I work for has a 2011 GMC Duramax/Allison. It started shifting funny-- getting stuck in certain gears, slamming in/out of certain gears, etc. Took it in to dealership--couldn't get it to do it so they put in a internal wiring harness for $2500. We got it back and it did the exact same thing. This time it was doing it when we got it to the shop so they were able to diagnose it right away. All it was was a $60 sensor. Can't remember exactly what sensor it was--maybe a park/neutral sensor? Of course they didn't help cover any of the $2500 wiring harness that did not need to be replaced.