New Truck Question

[deaf electrician]

I just bought a chevy silverado crewcab 1500HD with 6.0l and 4 speed transmission with 110,000mi. It has 3.73 and LT 265/75 16 size tires. When starting a trip this weekend down the freeway at 65 it was cruising at just above 2000rpm. Today on the way home I was driving on the freeway at 65 cruising at 1500rpm. I was estatic I thought this is how the truck should run. I then pulled off for a bathroom stop and got back on the freeway and it was back up to above 2000rpm.

 

Whats going on??? Shouldnt this truck cruise at about 1500rpm at 65 with 3.73 gears. I just put new spark plugs and air filter on it as well.

 

These trucks switch to 4 cylinders when cruising dont they. Is something not kicking in. Or does the ecm need to be recalibrated?

 

Any help would be appreciated. Thanks

[MaineRider]

what year is your truck?

 

 

I am fairly certain the the 6.0's don't have afm in the 1500hd's (kick into 4 cyl mode)

[deaf electrician]

sorry 2003. But why would it be able to drive for an exteded period at 1500 rpm and then switch back to 2000rpm

[wurgs]

6.0 does have afm but not in 03

[Stevens03]

AFM started in 2007 with the L76 motor

[[email protected]]

My 6.0l with a 4l80 and 4.10 gears is under 2000 rpms at 55 mph and a hair over 2000rpms at 60 mph. But, remember, mine has 4.10 gears, so my rpms should be higher than yours.

[deaf electrician]

The question is why am is the truck running at 2000rpm and then running at 1500rpm then switching back. Whats causing this. What determines engine rpm management?

[[email protected]]

The question is why am is the truck running at 2000rpm and then running at 1500rpm then switching back. Whats causing this. What determines engine rpm management?

 

Sounds like it's going in and out of tcc lockup, mine does it if I'm not going fast enough, but when I speed up it quits doing it. Mine will do it around 45-50, yours could be a little higher in speed because of the higher gears.

[GMSatan]

The question is why am is the truck running at 2000rpm and then running at 1500rpm then switching back. Whats causing this. What determines engine rpm management?

 

What about wind? If wind is blowing against you, it requires more power to keep the truck cruising at a certain speed.