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Message: [QUOTE="Charles, post: 85550, member: 103"] I don't know if it makes enough power at 1500rpm to pull an 8% grade with a 15,000lb load, in OD but it would not run hot flat to the floor at that rpm. It simply might not maintain speed. And I'm not sure where 1500rpm came from anyway. I don't know too many people running light diesels at 1500rpm on an 8% grade with 15k behind them... But.... in 4th or 3rd gear I'm sure it would trudge to the top flat-footed at 1500rpm with 15k behind it. Only problem might be keeping it at 1500rpm as it would probably start gaining rpm. An 8% grade is very tame for the hills around my house, and I routinely pull loads of 20,000lbs or more to and from my house, usually being equipment or hay. With the 1.15 on the 38R the engine generally pulls very hard down to ~1700 to 1800rpm before power starts to take a notable drop if I just had to wager a guess. Flat-footed at 1500rpm I expect my EGT would stabilize at about 1250 on the nose if you stayed in it indefinitely. When I hit the big hills on the north side of my house in the blueridge mountains, depending on load it will sometimes drag the engine down, and I'll have to downshift to maintain power. Sometimes from OD to 4th, then from 4th to 3rd at WOT in each gear on some of those grades. This is with a 300hp engine plugging along. Serious grades in other words. One particular stretch runs like this with a continuous uphill pull where I end up in 3rd gear most times, and this section lasts for [b]12 MILES[/b]... At no time however will the engine EGT exceed 1250 with me flat to the floor with the engine getting drug down through OD after a few minutes, then all the way down through 4th after a few more minutes, then finally stabilizing in 3rd gear, flat footed. The engine was tuned with the sole effort of extracting maximum horsepower while retaining a HARD EGT limit of 1250. So I'm a bit lost as to how you feel it some amazing happenstance that the truck can tow flat-footed up steep grades with a load behind it. Um.... that's precisely what it was tuned to do, while making the maximum amount of power possible without excessive amounts of injection timing for cooling. Lastly, there's no "tow tune". The truck is simply tuned to pull. That is it's job. There's no program selection, you just crank it up and go. One, permanently loaded program on the PCM. It probably makes ~300rwhp and is actually pretty quick even being a full service bodied 550. The throttle response is crisp and clean like a mech engine of similar power. [/QUOTE]