Transmission issues

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BlakeParker

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Hey guys. I have a 98 Z71 K1500 with the 5.7. I started having trans issues a little bit ago. It all started after I got on the road leaving my farm and was getting up to speed then on the 2-3 shift it hung and had a flare shift and hit some sort of low revlimiter.

I started doing some research and people were saying to do a jumper wire on the PCM. I made the wire and got it installed. Went for a ride and it shifted good then it suddenly started doing some more weird things. When I give it gas it hesitates then drops a gear and starts to go but at 2500-3000RPM it had some sort of a rev limit. I put the pcm woring back to factory and it was good for a few minutes then did the same thing with the low rev limit. But when in park it revs fine like normal.

So I’m not sure what to do as of now. New trans? New PCM? Where should I go first. Don’t have any issues on the code scan besides some things I’ve always had. My scanner only reads engine so might need the one from work. Any help is appreciated
 

Schurkey

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Perhaps a moderator will move this thread from "Transfer Cases" to "Transmissions".

Connect a REAL scan tool, look at engine and transmission codes and sensors/outputs/data
 

FourEightZero

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Hey guys. I have a 98 Z71 K1500 with the 5.7. I started having trans issues a little bit ago. It all started after I got on the road leaving my farm and was getting up to speed then on the 2-3 shift it hung and had a flare shift and hit some sort of low revlimiter.

I started doing some research and people were saying to do a jumper wire on the PCM. I made the wire and got it installed. Went for a ride and it shifted good then it suddenly started doing some more weird things. When I give it gas it hesitates then drops a gear and starts to go but at 2500-3000RPM it had some sort of a rev limit. I put the pcm woring back to factory and it was good for a few minutes then did the same thing with the low rev limit. But when in park it revs fine like normal.

So I’m not sure what to do as of now. New trans? New PCM? Where should I go first. Don’t have any issues on the code scan besides some things I’ve always had. My scanner only reads engine so might need the one from work. Any help is appreciated
Like Schurkey said, you gotta get a real scan tool and see exactly what the PCM is sensing and commanding.

I had a somewhat similar issue with the trans shifting too early and lugging the engine in 4th gear at ~25 mph. (No trouble codes)

Tranny shop that rebuilt the 4L60E said they couldn't find anything wrong.

The only thing I saw on my scan tool steup (TunerPro RT with the .adx file to scan the trans) was my vehicle speed indicating that I was going about twice as fast as actual speed.

A short comment by another member here told me to check the PCM for 4 low signal from transfer case even though it was in 2 hi.

Sure enough, rotted 30 year old wiring under the truck was causing that exact issue and I wouldn't have homed in on it if it werent for the scan tool.

Parts cannon would have been a complete waste of time, money, and effort.
 
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