I have a 2004 diesel pusher motorhome on a Freightliner XC chassis with a 300hp 5.9 Cummins ISB. I know they are not exactly towing powerhouses but I would like to do a tune to pick up a few more HP for towing. The motor is the same as the 5.9 in the Dodge trucks but the turbo & electronic controls are different so it's not that simple... any of you guys spark one of these up a little bit and have a tuner you can recommend that you are happy with the results? Pros / cons? Thanks in advance...

Hey Billy. The guy I bought mine from had put a tuner on it and on his first trip it put the transmission in a "Limp Mode" because of the increased torque. He took it off and I would still get a check trans light on every once in a while. They claim you could get a program that tells the trans it is still stock and will work with a tuner. I just bought a new coach with an ISL 8.9 and never looked back lol.

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Originally posted by JakeW143:
Hey Billy. The guy I bought mine from had put a tuner on it and on his first trip it put the transmission in a "Limp Mode" because of the increased torque. He took it off and I would still get a check trans light on every once in a while. They claim you could get a program that tells the trans it is still stock and will work with a tuner. I just bought a new coach with an ISL 8.9 and never looked back lol.

Yeah, that is exactly the kind of horror story I'm trying to avoid! I'm just looking for a mild tune but something reputable.

I had a Bully Dog tuner puck on my 5.9 pickup. It had 3 levels. 1st level was fine and I had it on for about 4 years. I tried level 3 once and it was crazy how much power it added. My biggest fear was the transmission failing.

I have a 2000 Beaver motor home with a 300 hp Cat and was hoping to find more HP to help in the towing and looked into tuners and what it would take for a few more horses and found out that it would cause a possible over heating problem and maybe trans. problems. I found out that on the older engines like ours need a much higher Cetane (like octane) rating to operate more efficiently. In the Cat manuals it noted a Cetane rating of 48 or higher. The ratings now are 38 to 40 at all stations. I've asked at some of the stations and they answer "What is Cetane" lol. I use a cetane booster DieselKleen by Power Services silver bottle. This is not a snake oil ad for their product it really really helped in the performance. Up hills much better, cruising at 1650 rpm with less pedal. I also use top tier sources like Chevron or Shell. My 2cents

Out of curiosity I googled 2004 Cummins 5.9 300 hp engine cetane spec needed. 40 minimum 45+ or better recommended. If your just filling up at the cheaper outlet stations you may be getting a rating of even lower than 39. Believe me it makes a huge difference to boost it.