asilverblazer

Looking at your data, the truck runs lean at full throttle. Not seeing it richen the mixture accordingly via the fuel trims though, not really studying it fully though. Based on what I see I'd be looking at fuel delivery.

The O2 sensor codes are for the downstream sensors. Those should not factor into the PCM's fuel trim and should not be CAUSING the miss fire, they could be detecting a lean condition caused by something else and are left to interpret it as a sensor low voltage condition. This would mean that the upstream sensors are either not accurately sensing the air fuel ratio - thus the PCM doesn't enrich the mixture accordingly, the PCM may not be getting an accurate signal from the sensors via a wiring fault, or the sensors are fine, the PCM is reading them correctly but isn't able to deliver the fuel volume needed due to a mechanical fueling problem, fuel pump, filter, or injectors (maybe dirty). I would watch fuel trims to see what the PCM is trying to do to correct the P0300. High fuel trims indicate its commanding a richer mixture vs. low trying to lean it out. A high fuel trim with lean O2 readings indicate an insufficient fueling problem.

I'm not a heavy guy and usually have a cross bed tool box in my trucks, just me and a full tank of fuel, all my half ton trucks have been about 6500 lbs, 60:40 weight distribution.

A carefully loaded truck (empty), with a carefully setup weight distribution hitch might be able to have a 13K lb trailer attached with 10% tongue weight carefully balanced between the trucks front and rear axles to a stay with in every rating on the truck. The only way to know is to spend some time at the scale. You must load everything you intend to travel with in the truck and trailer. Unhook the trailer and weight the truck. This reveals how much much weight you have left in the GVWR. That amount cannot be exceeded by the tongue weight of the trailer. You will also see how much weight each axle of the truck is carrying. Next, attach the trailer with out any weight distribution. Weigh again. You will now know what the GCWR amount is. It cannot exceed the trucks number. You can also see how much tongue weight is added to the rear axle on the truck, and how much it unloads the front axle. This won't really matter because adding the weight distribution system will re-allocate that weight among the axles. Next, the weight distribution system. Some amount of tongue weight from above will get put on the front axle and some will get put back on the trailer axles, that weight gets lifted off the rear axle. Lastly balancing the system, you will adjust the weight distribution hitch to maintain about 10% of your tongue weight from step 2 on the truck with out exceeding any maximum weight ratings, FAWR, RAWR, GVWR. You may find that it is not possible to do it. You may find that you're close or...

The size tractor you are referring to can EASILY be handled by a half ton truck. If you can't keep that load on the road with a new half ton, you shouldn't be driving anything other than a mobility scooter. It seems that everyone in this thread has a good grasp of the different weight ratings.

Sounds like improper fueling. Fix that first, the P0172 and P0175 codes. You've probably smoked the catalytic converters from running too rich. One of three likely problems (in no particular order): 1. Fuel injectors. 2. High pressure fuel pump. 3. Low pressure fuel pump. Perform a fuel injector balance test and check/monitor fuel rail pressure (high pressure pump performance) and fuel pump pressure (low pressure pump performance).

Proceed with caution, there are counterfeit parts... the new one may end up being worse than the old one. I'm not being critical of your course of action, just warning you not to assume that putting a new injector in (or any part for that matter) rules it out as the culprit of the problem. Be careful with the intake gaskets too. They are supposed to be replaced when you pull the manifold.

A couple things... 1. At the most recent oil change did the old oil smell of gasoline? Sometimes the high pressure pump leaks to the crankcase. I don't recall specs for fuel rail pressure but 700 seems low. 2. I would pursue injectors or fuel pump separately. You've done the injector balance test and the results do not indicate an injector issue. You can run the test as many times as needed to confirm that result. If you choose to replace any injectors do so one at a time with a genuine GM part. I would try the high pressure fuel pump first if the pressure is indeed low. I would not replace the pump and injectors at the same time, too many variables start getting introduced.

Pay careful attention to fuel pressure. A past thread with similar codes, went quite deep and it ended up being the high pressure fuel pump. Its a long read. Thread

For 'normal driving' the tire size doesn't seem THAT large. I would maybe consider a salvage swap for an axle with a more aggressive ratio. I would also have the pinion angle checked professionally because of the amount of lift. What failures required differential replacement? Why was the 'axle' replaced? Are the u-joints breaking or wearing out? Are the other parts breaking or wearing out?

I would have a new on hand - I would inspect the old one for damage and check wiring to it - if you are tearing it down to check the old one, might be just as easy to replace it while you're there. I don't have the actual diagnostic for it in front of me to confirm that a new knock sensor is the correct action for P0332. There is also an outside chance that something else could be causing weird engine "vibrations" that the sensor(s) are picking up as miss fires. If memory serves, bad motor mounts, loose components, accessory drive issues or other drivetrain faults such as out of balance tires even. None of these are nearly as likely though and I wouldn't consider until thoroughly diagnosing the knock sensor issue.

Depends on what the problems are. Driving style? Typical terrain?

Fuses, wiring harness damage?

1. What do you mean by "haven't really had much problems", either the truck runs fine with no check engine light or it doesn't. 2. Investigate the knock sensor first, the truck won't be able to adjust timing correctly without it. Poor timing can cause miss fires. Fix the EVAP line, obvious faults will complicate diagnostics.

I think those are both with in spec.

It took them over three weeks to fix a 'bad' battery? The battery probably went bad just like you suspect, in order to diagnose further they had to replace it. Battery replacement probably cleared all the codes and they were lost where to look next. No codes, no problem, come get your truck. What was being done during that three weeks?

Since when can GM not build a small block V8? 1. Failing lifters 2. Lifter bores 3. Misaligned main bores All within the last 4 years. If there was 1 thing in the history of GM that they could do right it was a small block V8.

Probably be real easy to find a 3.73 axle with G80 in it, bolt on and go. (Tune update of course.) 4.10 would be just as easy to do but harder to find. The 4.8 was never a torque producer, power only really exists spinning it fast. I'd select mods to compliment that, a higher revving cam (within reason) wouldn't be a bad choice. Top end kit, long tube headers, transmission cooler, gear swap, tune. Cam shaft selection would take the most careful thought. Lastly, depending on the cam maybe a torque converter. For towing, the transmission cooler I'd recommend if your truck doesn't already have it an electric trailer brake controller and good receiver hitch. Otherwise all the mods ought to make a fun little truck to drive around.

Has anyone tried adjusting the trailer brakes to see if any improvement can be had? It's not recommended but I always adjust my trailer drums to provide 'heavy' drag when spinning the wheel/tire.

Seems pretty common sense to me, a gooseneck and fifth wheel both place the trailer tongue weight in the same location... Camper dealers are notoriously poorly educated (dumb). Never take advise from them regarding what you can or cannot tow, you'd be better off to ask your neighbors cat.

No... but to be clear... Weight on what tag? The trucks tag specifies maximum weights that can be placed on/behind the truck. The trailers tags indicate the maximum weight that can be carried by the trailer and it's axles. The actual pin weight of a particular trailer can vary based on what you put in the trailer and where you put it. The key is that when the truck and trailer are loaded as you intend to travel to weigh the combination at a truck scale. You should get three weights: 1. Steer/Front axle weight 2. Drive/Rear axle weight 3. Trailer axle weight 1 and 2 cannot be higher than the corresponding GAWR on the trucks sticker. 1 and 2 cannot add up higher than the GVWR on the trucks sticker. 3 Cannot be higher than the trailers axle ratings on the trailers sticker. 1, 2 and 3 Cannot add up higher than the GCWR on the trucks sticker. To determine the actual pin weight that cannot exceed the 2865 lbs, the trailer would have to be unhooked and the truck re-weighed without it. The sum of 1 and 2 with the trailer, minus the sum of 1 and 2 without the trailer is the pin weight.

Above is the only other reading I found on the topic... Nothing I read seems to follow a path that results in replacing the switch.