My opinion
I have an 04 crew cab short box 6.6 with Allison- its a 5 speed, they went to a six speed in 05. Yours is most likley an LLY version engine in that 05 same as my 04. I get 14 around town and about 16 on the hwy empty. Towing I get around 8. As many have said you keep the RPM's under 2k and the mileage is much better, however with the 5 speed trans 70 mph is about 2200 rpms.
Fuel filter is every 15k miles, along with the spin off trans filter. I change mine every 10k when i change my oil. Cost about $135 doing it yourself for all three.
You should know there are many reported problems by owners of this version of the duramax with overheating when towing heavy- only the LLY version engine is reported to have the issue, however I tow 12k fifth wheel with mine and have never had an issue. I ae 100k plus on mine with only minor problems. You should also know the transfer cases have a pump rub problem that needs top be fixed also by replacing the pump cover in the tranfer case. Some truck will make it 200k before the pump rubs through and some rub through in 80k. You can read alot about these on the duramax forum- http://www.dieselplace.com/forum/index.php?
However based on everything, I would not buy a diesel again unless I was using it to make a living.
Good luck with whatever you decide.
I have an 04 crew cab short box 6.6 with Allison- its a 5 speed, they went to a six speed in 05. Yours is most likley an LLY version engine in that 05 same as my 04. I get 14 around town and about 16 on the hwy empty. Towing I get around 8. As many have said you keep the RPM's under 2k and the mileage is much better, however with the 5 speed trans 70 mph is about 2200 rpms.
Fuel filter is every 15k miles, along with the spin off trans filter. I change mine every 10k when i change my oil. Cost about $135 doing it yourself for all three.
You should know there are many reported problems by owners of this version of the duramax with overheating when towing heavy- only the LLY version engine is reported to have the issue, however I tow 12k fifth wheel with mine and have never had an issue. I ae 100k plus on mine with only minor problems. You should also know the transfer cases have a pump rub problem that needs top be fixed also by replacing the pump cover in the tranfer case. Some truck will make it 200k before the pump rubs through and some rub through in 80k. You can read alot about these on the duramax forum- http://www.dieselplace.com/forum/index.php?
However based on everything, I would not buy a diesel again unless I was using it to make a living.
Good luck with whatever you decide.