2003 GMC Sierra 2500 HD Questions

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Put in new radio and battery, fuel and oil gauges are not working
Horn works normally when truck is cold and not running. Works when truck is started. Stops working as soon as transmission put in D and brake pedal released. Will not work again until truck turned off and cooled down. I have changed the horn relay- no change. What next? Scan tool?
I turn it off, try again, it may take 2 or 3 times then it will start normal. It sounds like the starter is cranking, but it either doesn't start, or it starts, runs rough for a second, then it runs fine
only happens in 4wd lo or hi
I have a manual dual a/c controller. A couple months ago the lights went out on the controller but still worked fine. Then right after that is was blowing hot on the driver side and cool on the passenger side. But after starting it over and playing with the controller it started working fine again. Now it's not blowing at all and making a ticking sound behind the controller or passenger side dash. Does anyone know what is causing this or what I need to fix?
so my dad took his truck to fix his starter and he got it out and today it started having low idle problems which he said has never happened before with the truck any idea's before we go waste money?
I went to pull a buddy of mine out of the mud last week, and then after that I noticed that when I give a fair amount of throttle, the transmission, and engine get really quiet, and it takes forever to shift. Also when I am running down the highway over 65, and I give it throttle, the engine also goes really quiet and loses power, and then lugs back into power when I let off of the pedal. Is this transmission problems? I just don't want to take it and be charged to hook it up to a computer.
Changed filter it started shut of won't start
My diesel truck just had the cluster replaced now when I drive it for more then 50 miles, the check oil pressure, low oil pressure comes on and one instance, the truck actually started to down gear! Help! What could be making this happen? should I replace the oil & filter, oil pump or something more serious??
Differential ??? Or e brake ?? Or what .
Just bought this truck only thing the computer said was " service brake booster". Ok went on a 300mile trip about half way I was stuck behind a car going 65mph went to pass and the truck made a noise I lost power and the check engine light came on. I couldn't go over 50 to 60 made it to a auto parts store and they read my check engine light. It said all 4 O2 sensors had low current I undid the battery and reset the computer. Everything cleared and the truck was running good again but the third time I turned on the truck my battery gauge maxed out. I undid the battery again and again everything cleared up and truck was running good again. Took the truck back 300miles home made it half way again the check engine light came on I lost a little power and my battery gauge maxed out again. Got it home finally check engine light still on and service brake booster and the battery gauge was past the red zone my fog lights were dim and my headlights were brighter. Can anyone help me and tell me what's going on?
dash cluster went crazy truck stopped running
I replaced the water pump and test drove and worked great. I stopped to check for leaks and found none, but the temp started rising so I drove straight home. I them let truck idle and the temp went to 210 and them to 260.
OK, so I have this truck with an initial issue of a faulty fuel pump, improper fuel read on gauge and no oil pressure. I replaced the fuel pump/sender and the oil pressure switch. Those are both fine and now work great. But, now I have this new P code pop up. I have replaced the CMP with a BWD part from Oreillys. This didn't fix it. Looked deeper found a few wires on the CMP plug were peeled back and touching each other. Taped these up, reset the comp and it was great until after about 30 miles when it started over with the code again. The pins and the socket terminals look and feel fine (not ruled out yet) but eyeball looks good.

Truck will idle and run great, drives all day no issues. It is hard to start and sometimes it sounds like an engine that has hydra-locked (this is the best way i can decsribe the symptom
). This will happen for about three attempts to start then it will finally start.

What I can see of the reluctor wheel the teeth are fine and no obvious signs of contact with the sensor itself. (just to rule out)

When scanned with a 2014 Verus D10 series scanner, the codes only pull p0342 under the drive line. Looking into the system a bit deeper, the ABS system pulls a code also, c0550. That code shows an ECU/CCU Malfunction. Is this a stand alone subsidiary ecu or is it part of the main ecu. If it is internal would this point to the main ecu as faulty and thus demand a replacement? I have not ruled out the terminal contacts at the ecu yet, so I understand this still needs to be done. But, So far I have to start leaning to the ECU.

This truck was driven at least 50k miles with the initial issues before they were looked at and corrected. The previous known repairs have been, repairing/replacing a broken/cracked bell housing and the transfer case busted off the tail housing coming to rest on the cross member (signs of heavy wear at the crossmember-not sure how it was driven in this condition). The front wheel was about to fall off due to poor ball joints and the outer tie rod end loose. Not sure if ALL this vibration chaffed some wires or simply knocked these systems out directly. Either way it is not good.

I know this a lot of information but i just want a good solid educated opinion before I proceed to ECU replacement/reflash.
One day they worked, the next they didnt. My radio n CD player seem to be working just as before but they are not putting out any sound. I even tried the DVD player in the back as well as the ONSTAR, Neither of which, worked. What do I have to do or attempt to fix to get them to work?
Thank You
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