I have an '04 GMC Sierra 2500HD Crew Cab 4x4 6.0 liter.

It was previously my dad's and he never had any problems with it at all. The week I bought it the check engine light came on even though it was running fine. After driving it for a while the tach started acting up. It seemed like it got stuck and it was registering higher than it should have been. Even though it was idling fine, the tach was up to 5000.

Then the light went off.

Then about a week later the light came back on and it seemed to get stuck at 3rd gear. I would get up to 55mph and the tach was reading about 4000 rpm. So I turned around and parked it for the day.

After work I got back in it and the light was still on but it was driving fine. I took it to AutoZone and they said it was showing code P0758 - Shift Solinoid Electrical.

After driving it a little longer the light went off and stayed off for about a week. It was driving perfectly.

Well tonight the speedometer started acting up. The check engine light isn't on. It was reading 30mph higher. If I was stopped it was stuck at 30 and when I was going about 30 it was reading 60.

So its sitting in my driveway after that and I'll see what it does in the morning.

After searching around the net, I have read that it could be the ignition switch. Does this sound like the ignition switch or something else? If it is the ignition switch, any idea how much that would cost to have replaced? Is it really complicated or could it be a DIY job?

Any information is appreciated. Thanks!

 

You should post this in the Silverado forum and also maybe send Argon a private message about it.

 

Well,you have 2 problems,I believe...The speedo thing is a problem itself...a bad cluster.03's and 4's especially have cluster issues.
As for the shifting,if you have that code,its most likely a bad shift solenoid,or the wiring going to it.
if the ignition switch were bad,you'd have a ****load of codes

 

Thanks for the reply Argon. About how much do you think it might be to fix it?

As far as the shift solenoid, is there anything I can check myself, or is that pretty much a mechanic/dealer problem?

 

The cluster isabout 285 bucks,and about 1 hr labor to install and program it.

the shift sols....are very tuff to diagnose...no,make that impossible,as they stick and are hard to catch stuck....the best thing to do is just put em in...2 sols,put em both in together.,
If you can put atranny filter in,you could put the sols in...

 

Thanks for the info Argon.

The tranny issue seems to have fixed itself because I haven't had that problem in over a week and its been running great. So I'm not too worried about that unless the Check Engine light comes back on or I notice odd shifting again.

Do you think the tach issue and the speedo issue are the same thing? Maybe it was just a coincidence that the tach was acting up when I had the shifting/check engine problem.

 

Well the transmission issue came back and the light came back on.

Dealer says its the ignition switch, so that is being replaced today. So I don't know if it was giving more codes this time or not. He doesn't seem to think that's related to the speedometer getting stuck. I'm waiting on the instrument cluster for now. Do you think it could all be related? It all started on the same day, so that's what makes me think its related.

 

possible...but doubtful...We've just seen too many bad clusters

 

Well the ignition switch didn't fix the problem anyway. On my way home yesterday the light came back on and the shifting problem started again.

 

take it back to that dealer...they said ign switch and were wrong...make em refund that towards fixing it