mjm-1957

Have the dealer drive it with GDS 2 installed and command the tcc off 100% and note if the shudder still occurs. I am bettting the 456 clutch is slipping, not the converter. Three defective ones in a row??? Doubt it. I am the transmission guy at a GMC Buick dealer and have seen this before. They can also monitor the slip speed with the GDS while commanding the TCC on 100 %, will tell them which way to go.

It is a LIN bus communication error with the ECM. Bring it back to the dealer and let them fix it.

Welcome to GM. I have a stack of bad fuse boxes under my bench for all sorts of problems. I keep them for all the fuses and relays as spares.The high speed wiper relay is also internal and goes bad quite often. That fuse box is not cheap either.

Those numbers you listed are just the codes for recalibrations that are done and submitted to GM so the dealer can get paid for doing the update.You need to see the actual TSB number or the Doc Id number of the update they are doing to see what it is trying to fix.

The horn relay is internal to the underhood fuse block. If the wiring checks out and the air bag is good, than the relay may be shorted and keeping the horns on.

What engine do you have? L5P or L96?

Are you pressing the bearing back on or beating the crap out of it with a pipe? Also are you using a GM bearing or aftermarket?

Look at the center electrode porcelin, its not straight and square like the others. I would replace that plug with a new one put it back in number six and run it for a while and then check again. We have been getting alot of defective AC delco parts right out of the box lately. Possibly a boot leg knock off counterfit part.

Replace the master cylinder. We have had more than a few like this.

Check the crank sensor connector.

It will also disable itself when a lifter fails and bends a pushrod.

Check the other hub bearing . They can fool you sometimes. We run them in 4wd on the lift and put your hand on the tow hook in the chassis . You can usually feel a rough bearing right threw the hook.

I'd be looking hard at the head gaskets.

Bring it somewhere else for a second opinion. Thats not common at all.

You need a new mechanic. Check fuse number 24 in the underhood fuse block.