Canadian Hummer Club Forums

Since I'm still on my transmission high, also had another question,

When one city drives , is it best to drive in "D" ? Or alway leave in "OD"

I always get in trouble for saying this but i like to keep my revs high rather than low. i find the 6.5 lugs a bit being a lower powered engine and a slow turning water pump doesn't help with cooling ups and downs either. It my opinion that this is why so many of these engines fall apart way too soon and crack up because of constant lugging and temp fluxuations. Diesels like to run steady hot and they achieve the best performance and longevity at peak RPM and peak temps.I think its real important to have good hot oil to run out these trucks or shit will happen sooner than later. Look at all the dead engines we have seen in the last 20 years that died of heat stress often before they even warmed up, which takes about an hour on the highway at 60mph to get the oil hot enough to run.
I find i achieve a more stable performance and temps keeping between 2400rpm to 3k rpm range. I run third gear around town and on highway up to about 55mph. Above 55 i switch to the OD so i can make 80-85mph at roughly 3k rpm to keep in the passing lane. Truck is totally stable in that state all day long, just dont shut it off when you gas up and make sure you run your fast idle whenever stopped with a hot motor so it doesn't heat soak with no air on the coolers.. Interestingly the published top speed on the H1 is 84mph so i imagine running close to that gets the best you can get. Aerodynamics are an inhibiting factor though!! LOL
As far as the trans is concerned the sooner you hit lock up the better it is for the trans fluid temps. The 4L80 has a real crappy and weak OD gear so i avoid using it unless needed for steady cruising on down the highway at speed. Around town 3rd gear plus lockup is great. The third clutch is pretty beefy in the 4L's  as its designed to tow stuff.
Oddly, you would think with higher revs etc your fuel economy would suffer but i haven't noticed a big change, in fact maybe some improvement in some cases around town.