mjm-1957

Have the dealer hook up GDS2 and monitor inputs to the lift gate module and the bcm. Probably going to see something triggering the actuator, such as defective switch or shorted wiring harness causing an unwanted ground.When it is doing that it shouldn't be too difficult to see what is causing it.

How about you see what code is stored in history before you go off on a wild goose chase. Could be anything, steering wheel position sensor, low brake fluid warning, intermittent wheel speed signal etc etc.Right away your pulling the dash apart and checking grounds and replacing the battery.

On your RPO list what is your brake option? And are you sure you have a 454? Most gas engines were 366 or 427.

Send it out to a rebuilder and have it overhauled.

Did you check the injector connector with a noid light? The connector has 12 volts on one leg and the ecm grounds the other to fire the injector. The noid light plugs into where the injector would go and shows if the ECM is providing power and ground.

Get up to highway speed and Shift into neutral when safe to do so and start applying the bakes, and if it still does the pulsation its in the brakes.

Guess your going inside.....

Take the rubber plug out on the tail housing and get a mirror and a light and see if the snap ring that holds the rear output bearing is still in one piece. That snap ring can break and let everything move rearward and possibly cause the issue you are having.

If you are in 4w high or low and not getting any action from the front driveshaft im sorry to say you will have to go inside the transfer case. When you had the encoder motor off did you try shifting it manually?I have had a few with broken shift fork parts and also a worn roller that rides on the cam not allowing full motion of the shift fork but it also was grinding, and you didnt mention any noises.

The oil pump is only there to provide lube oil. The clutch pack only is used in auto 4wd.

The clutch pack is applied mechanically.The front and rear driveshafts are locked together in 4 low, thats why I asked what it does in that range,are you sure the front axle is engaged?You should not be able to turn the front driveshaft if the actuator plunger is pushing the shift fork all the way in. You can also take the actuator out and physically move the fork with a screw driver and make sure nothing is binding or broken.Hope this helps.

What happens in 4 low?

Why would you buy a 1500 to tow a horse trailer?You should have stepped up and got a real truck,2500 or 3500.

Get a small telescoping bendable mirror and have a good look at the squirrel cage

You dropped an acorn or some other crap into the blower motor. You can't believe how often this happens.

Sorry to hear that about your dog. Had to put my German Shepard down from liver cancer and it wasn't easy. Felt like losing a member of the family.

How is that transmission holding up?

Get that thing running again and have a blast with it and your kids.Looks really good for being uncovered and outside all that time.

We have been seeing that more and more lately on the 2500 and 3500's that are towing heavy trailers and or used in commercial applications. I have personally been involved with three of them so far and it is usually just one side as Rdelfleet has said.GM has us changing the caliper and brake hose on the side with abnormal wear or brake temps.Of course a pad replacement and a rotor refinish and a thorough cleaning and lubrication of the caliper slides. Haven't seen one come back after doing this.

If it has a transmission dipstick its a 6 speed. The 8 speed has a fill plug on the case and no dipstick.

I am a mechanic in a Buick-Gmc dealer and have not seen many valvetrain issues on the 6.0's. The engines with AFM is another story altogether.I just finished a camshaft,lifters,vlom,and one cylinder head on a 2015 yukon with a 5.3 that had 37,000 miles on it Wednesday and today got a 2016 Yukon XL with 31,000 miles on it running on seven cylinders and making alot of valve train noise on the right bank, I pulled that valve cover off and have a broken exhaust valve spring on number 6 which is an AFM cylinder.It is almost always a cylinder with deactivation which either break the lifter or flatten the cam out.Both engines were clean inside and obviously maintained. We are seeing alot of theses lately.I am waiting on parts to finish this one Monday and hopefully it is just a valve spring on this one.

Check out document ID#4881898 (can't provide a link) If you google service update 17388 it will bring you to the correct document.It says it is for the pressure relief valve in the rear body allowing water intrusion into the cab on 2018 siverado and sierra, we have two 2016's in the shop right now leaking from the same area, carpets are soaked and stinks of mildew. It apparently affects other years also. If you remove the rear seat and trim , you can pull the padding away from the rear panel and you will probably see a puddle and rust stains from the lower portion of the vent. If your truck is brand new bring it back and give them this service update and doc id number.Let them deal with it under your warranty.