2010 Silverado V8 4.8 L
i was pulling some bushes out and at one point, I had the pedal floored (strong bush) but the rpm only was at 1800 and the wheels weren’t spinning. I put the truck in neutral, pressed the pedal down, and was easily able to red line the gauge. I then put it in drive and again the truck wouldn’t go above 1800 rpm and the bush wasn’t budging. Is this a safety for the truck or is this a problem?

Sounds like torque converter stall but that'* pretty low.

It'* a self-preservation thing. It might also be an element of torque converter stall point. The 4.8 is a great engine, a little low on torque, but a great engine. I've had a few in Penske GMC 3500 Savannah single rear wheel box vans with the 4.8 . They work great in that environment, happy to rev to make power, but those are set up with a lot of self preservation in mind. Regardless of how it is programmed for preservation, the torque peak is at 4,600RPM. It is meant to keep things moving, and not so much to pull stumps.

Does the fact that the limit is at 1800 rpm and not 4600 rpm as you stated indicate a problem with the torque converter? I have towed a car with this truck previously and had no problems. I’m sure that the engine was running over 1800 rpm. I would think that I wouldn’t be able to climb a hill if the truck’* limit is that low.

Torque converter stall is not RPM limiter. Think of power braking.

So is this torque converter stall at 1800 rpm considered acceptable and nothing for me to worry about? Do I simply need to use a larger truck to pull out the bushes 🤔

Normally I wouldn't expect the wheels to be held so tight as to stall the converter unless maybe you are trying to pull them out easy and the wheels are on concrete.
Had you tried a small amount of slack and snap it?

I did have the rear wheels on my concrete walkway (the truck is only 2 wheel drive). I had the chain attached to the bush probably only 3 foot away and attached it to the underside of the hitch so there was no wheel slip. The harder I accelerated, the more the back end would be pulled downward to the ground. I did not try to jerk it out and after giving it some thought, I wonder if I would have been better off turning off the traction control switch. And before I forget, I truly appreciate all the information that you guys have been providing me.

I'm still a bit surprised at that low stall speed.

First: The stall point of a torque converter is completely unrelated to the torque peak of an engine. Torque converter stall point is the engine RPM at which a given amount of torque from the engine will not be able to spin the input side of the converter any faster unless the output side of the transmission (drive shaft, therefore wheel(*)) starts to turn more than dead stop.

In the old days, the stall point was set by the design of the converter versus the torque output of the engine. Notice that I say torque output of the engine instead of torque rating of the engine. Temperature, altitude, fuel, and a few other factors play into how much torque an engine is able to produce. Let'* say you have a torque converter on a turbo 400 transmission behind a Buick 350, and it stalls at 2,000RPM. Leave every single thing alone, swap the 350 for a 455, and that same converter in front of the same transmission in the same vehicle will stall at more like 2,200RPM because the bigger engine has more torque.

Now, in your modern techno-marvel truck, the computer is programmed to help the vehicle survive doing things that break the vehicle. In your case, I'd bet a nickel they programmed it to not allow more than a certain RPM from the engine until the drive shaft turns. Either way, I think on the 6-speed automatic, 1,800 for a stall point is probably about right. This eliminates some heat as well as large RPM variations when the torque converter clutch locks and unlocks.

The fact that the engine'* torque peak is at 4,600RPM and the 0MPH stall point (whether prescribed by parts or programming) is 1,800RPM just tells us that your engine will never produce full torque at a dead stop and your transmission will never have to deal with that. This is common. It also saves the transmission and driveline from a bunch of stress.

Yes, the stall point of the converter is engine RPM versus vehicle stopped and nothing else turning. Once moving, the whole RPM range is available depending on speed/gear/programming/etc. Did you notice while towing a car that it starts out okay enough then becomes more happy and willing as you pass 4,000RPM? That'* because you are getting into the range of RPMs that your engine is able to make more torque.