The allison transmission is used to those shift points , drive it for a few days without the trailer (not in tow mode) . I bet that the shift points come down a bit .

 

Today's drive was without the trailer. I tried it in both TH mode and non TH mode, it shifted at the same points. It clearly is shifting at the higher shift points commanded by TH mode. The cel light is not on, but I will have my buddy that owns his own shop, and has an 04 duramax, scan it for me with his professional grade scanner to see what it shows. The fuel in the tank is about 2 months old, and I always run injector lubrication additives. I have a second tank in the box that I run algicide in, as that tank sits with fuel in it for longer periods of time, but I run the bio diesel additive shown in that tank. I've owned the truck for 6 years, and all I've done is regular maintenance (as described in my opening post) and the truck has never given me an issue. The batteries are not old, but the truck does sit for long periods of time. I will throw the charger on them and take it for a drive. The gauge on the dash shows its charging at 14V. The fuel filter was a new wix unit in the spring. The truck gets a new fuel filter every second oil change.

 

How does it pull at WOT?
If it's down on power it'll affect the shift points.
Diesel stuff that sits around can glow algae in the fuel. That'll plug your fuel filter.
I treat all my stuff usually once a year with some biocide treatment, it has the same active ingredient as antifungal creams.
The stuff is expensive, $25 a pint but you only need a little bit.
Here are a few other things to check
fuel pressure @ WOT , if you change the fuel filter cut it open and see if you find anything.
scan it for codes.
smoke check it for boost leaks
make sure the MAP sensor is clean and not sludged up

 

Algae is a mf'r!!

 

Put that biocide in the tank and that takes care of it. A lot fuel treatment tries to imply it'll work for algae but it doesn't.

 

Amazon.com : diesel fuel biocide

 

Those wix/napa fuel filters are junk, i've seen more problems with those and more fuel systems replaced with those plastic pos style filters. Stick with the white OEM ones or the parker/racor that's who made the OEM. Gm has a new blue filter that replaced the parker/racor I would shy away from that one to, they went cheap because the L5P has a diferent filter now.

 

I noticed right away that the Wix filter was composite. I've always run the gm stuff, and never had an issue. I associate wix with quality. Huh...........

 

All I have ever used on my 07 Dmax is Wix fuel filters. Never had one problem. Maybe I am just lucky.

 

Scanned the truck today. No light on the dash, but the scanner showed an engine temp code and a trans temp code. Typical diesel hates getting up to temp. Cleared the codes and ran it around the block. All back to normal. I will look at replacing to two sensors with new GM stuff. Thanks guys.

 

A friend of mine has an 06 and early on he had thermostat problems. Had to end up changing both of them. It was not an overheating problem but rather not being able to come up to temp because one or both hung open.

 

This thread raises a few questions for me:

Has anyone converted to the CAT fuel filters?
If so, is it worth it?

Is a cetane additive necessary in the winter or any time?

 

Don't waste your money.
I see a lot of high mileage trucks, I have a 7.3 right in now with close to 700k on it, I had a 2005 Cummins 5.9 here earlier this week with 475k on it, they made it that far without upgrading the stock filters. I've been around diesel trucks and equipment for 40 years and never seen a need to run any additives except biocide and anti-gel when they are obviously needed.

I'll add this: I have looked at some of these additives, I pulled their MSDS sheet and had my brother who has several degrees in chemistry and is a MIT Ph.D read them and tell me whats in it, it's alway the same answer from him, "a bunch of bs"

 

man you should smell an oil tank that has algae in when we have to cut it up to clean it out for scrap.

Some of the foulest septic tanks is a close comparison LOL

 

If you fill the truck on a regular basis is there a need for biocide?
Is there a prophylactic amount on regular basis?

 

Both tanks are left full all winter. The truck rarely gets used in the winter, so the fuel sits as well.

 

had algae in my RV when I got it 8.3 cummins was always changing filters full of black shit put the biocide in it and with in two tanks and two filter changes was all good it gets it twice a year weather I run it or not, cheap insurance and with every fill up one gallon of cheap two cycle oil ,get almost 2 more miles to the gallon