Ray Pickle

I have towed that route and had no problem maintaining speed far above what TFL accomplished. Clearly the truck will perform much better than their representation. No one that knows anything about towing would allow their truck to lug like they did in their test. Understanding the desire to test uniformly, thus leaving the truck in drive, the ultra conservative tuning by GM caused the poor result. Another poster alluded to thermodynamic characteristics of small block being the reason for this tuning. My own experience indicates normal operating temps for coolant and trans temps ascending that grade at higher rpm. Further I see no significant differences in cooling capacity between the big three that would require the GM trucks to limit engine speed under those conditions more so than the competition. I would sure be interested in a more in depth reason for the tuning parameters GM has chosen to use in this truck. I don't see where a 10 speed would change the result much with the tuning parameters GM is presently operating this engine under.

Apples and Oranges

Minor point of clarification: it appears the old 6.l wasn't nearly as pronounced of an issue as the 6.6

Iam not an engineer but have a little experience in the field of auto repair and basic understanding of thermodynamics, and would love to hear how Ford has managed this issue better. Further I have curiosity as to what has negatively impacted the new 6.6 vs the old 6.0 which apparently didnt suffer from this problem TFL tested a 2015 and it maintained 4 to 5k throughout duration of ascent other than the last mile where it lost rpm to 2900 before downshifting and then revs to the summit. Just rewatched that and they mentioned the programing issue. If it was trying to protect itself from being outside safe operating parameters the downshift is hard to explain- same as the new 6.6.

If the calibrations of ecm are attempting to deny downshifts under the circumstances of TFL test I will stick with my comments on poor programming parameters. After rewatching the footage and seeing the truck downshift just prior to the peak of ascent after allowing engine to lug to approximately 2k "not good". I am convinced that poor programming is the issue. As another has posted and I agree- the cooling capacity of this engine platform is robust and at least the equal to both Ram and Ford . There is no mechanical reason this powertrain combo cannot deal with the Ike in its powerband- 4 to 5500 rpm under most circumstances. Do you have powertrain calibration data indicating that heat soak or other parameters are at play actively causing this programming need? If so do the numbers indeed indicate the 6.6 is poorer at heat dissipation than Ford and Ram? I am genuinely curious and not above learning something new, just based on my own experience and actual use I find it hard to believe.

It will easily hold 3 to 4500 rpm up the ike with more weight than you describe. Further the engine/cooling system will be happier in that range than lugging it and beating the bearings out of it as a result.

However to your intial comment- the engine cannot. Further the ecm is by not commanding the downshift is in fact defacto denying it. The programming is the issue- I have towed the "ike" more than once and in similiar weather variables to the test conditions along with warmer days and have never been denied a downshift. Surprisingly the truck would hold 2nd gear at redline if I desired on the steepest sections or slowly lose speed and rpm ascending in 3rd towing 12k 5vr. Trans temp would creap as you would expect if I beat it like that so I choose not to. But neither trans nor coolant temps went anywhere near the danger zone. I typically choose to tow it at a more drivetrain friendly 40 mph ish range.

Curious what that means?

Where all 5k of miles using 700 gallons towing? If so , that indicates about 7.8 mpg! Thats seems to indicate some pretty aggressive/high speed towing habits for that weight or a high % of hilly terrain. If there is any non towing miles in that figure it is more perplexing. High rpm high speed towing will probably burn a little oil and may be normal. If that is not the case I would be concern about the relatively poor mileage and oil consumption.

What TFL comparison clearly indicates is poor programing algorithm of transmission mapping. Any experienced driver would never allow engine to lug like they dis in the test. For uniformity of testing I understand why they did it, but it in no way reflects how the truck would perform driven properly with its power band.

20' z71 ccsb lt gas- everything but sunroof. Payload 3552

Power band of most diesel engines are much narrower than that of gas engines that is why they traditionally have more ratios. A 10 speed in a h.d. gasser may offer incremental improvements in drivability and efficiency possibly at the expense of long term reliability. The constant shifting/ potential hunting is what causes heat and we all know what heat causes in an auto trans.

The optional 7.3 is 10% larger in displacememt than 6.6 makes 7% more horsepower and less than 3% more torque. Not many efficiency test done on these but I recall TFL doing a comparison on these and 6.6 was more effecient both towing and unladen. I think the difference was fairly significant based on % differences. Can't recall specifics but I do know they where different days and different trailers so exact conditions where not present. I seem to recall the GM was a heavier trailer?

Looking at diesel forums where guys are hauling similiar weights to me they seem to report 9.5 to 11.5 mpg with the occassional outlier. I have tanks towing a 12k fiver ranging from 7.2 to 9.9 with an overall average towing number on most trips, those over 1500 mi at 8.8. I am betting my average speed is probably slower than the diesel guys. I intentionally try to stay at 65 or slightly less in an effort to maximize my economy. I would be very curious to see a simultaneous test done by someone to see what the real comparative Differences would be. I would guess 20%, in my area of country diesel is 10% higher on average thus closing the gap a bit for fuel alone not considering the other costs.

I would disagree that fuel costs would be 1.5 to 2x greater. Depending on region fuel cost differences can bring them close together on a cost per mi. calculation add def, maintenance, reliability and gas looks pretty good. This obviously assumes you are towing within capability of gasser. Its a separate discussion/ consideration if you NEED the diesels enhanced capabilities.

Agree with your observations and conclusion.

Lower 1st gear multiplication will be a plus and possibly better unloaded cruising economy. It will not be a significant step up overall.

Arbitrary need for 10 speed? Logic? Clearly not.

I won't consider a new truck until they offer a 15 speed! Lol. How in the world did we ever survive with those old THM350 and 400 transmissions back in the dark ages. C'mon folks a 6 -8- or 10 speed in a gas engined truck that operates best between 2 and 5k rpm have very small practical comparative operating differences. Evidenced by performance of F250 with 7.3- 10 speed equipped with 3.73. (Not4.10)

Not so far in 35k.

Lowest warranty transmission over time has been the 6 speed in h.d. trucks I would assume that will continue based on additional enhancements made in 2020 additional clutches etc.

2020 2500 cc lt has a payload of 3552. Most gas optioned 20' and up 2500 will fall between 3200 and 3700 in payload. Obviously lower optioned trucks have the higher payloads.

Replaced on 20' about 2 hrs.

Remote start