2004 Chevy Silverado Down Shifting

[straffordengineer]

I have a 2004 Silverado with a 4 speed tranny and a 5.3 engine. I love the truck but I hate towing my boat with it. If I keep the cruise OFF, it will do fine and I get about 13 mpg. If I leave the cruise ON, it will down shift to 2nd on almost every hill and shoot my rpms up to almost 4000. My mpg suffers and I get about 11 to 12 mpg on the same trip. I have tried Tow Haul, running in overdrive and without overdrive. It doesn't matter. It seems if I can prevent the excessive down shifting by driving with the cruise OFF, then there ought to be some way to de-activate the downshift to second while in cruise. Any ideas?

[n2ratfishin]

My last 4 speed was a 08 Avalanche with a 5.3 and 3.73 G80 rear end. I always pulled in third (1-1) and it would always downshift hard pulling if using the cruise control. The cruise control would kick off under a load on big hills on that one and the 14 I traded for with a 5.3, 6 speed and 3.08 gears. I pulled in 5th with the 6 speed but there was no 1-1 ratio with that one.

Both of my Tundras have enough ummph to pull in 5th (4th is 1-1 with a 4.30 rear end) and the cruise has held steady as a rock rarely kicking down to 4th even pulling a 520L 2000 miles. I've always got about 12 MPG towing on the interstate no matter if pulling with a 4.0 4-Runner, Chevies, or my 5.7 Tundras. I use the heck out of my adaptive cruise, may get a MPG better not using it?

GM's 1/2 ton issue is they go for the extra MPG. You may and try swapping for a 4.10 rear end? I know the 97 Chevy I had with a 5.7L and 4 speed hardly ever downshifted with that rear end. The downside was it got 12 MPG empty or loaded.

[jbh3]

On my 2000 GMC with 5.3/4 speed/3.73 G80 rear I always pulled in 3rd and with the tow/haul activated. Lots of hills in East TN. The only time I shifted to D was the few occasions I ran on the interstate. Trips were never long enough to use cruise. Can't comment on gas mileage as I never check.

[Nightmare]

...If I keep the cruise OFF, it will do fine and I get about 13 mpg. If I leave the cruise ON, it will down shift to 2nd on almost every hill and shoot my rpms up to almost 4000. My mpg suffers and I get about 11 to 12 mpg on the same trip. I have tried Tow Haul, running in overdrive and without overdrive. It doesn't matter...

I have an '06 and pretty much same. I make a couple long trips south each season. I've done various scenarios to experiment and concluded, leave in tow/haul - set cruise - and let'r eat. The difference over the course of 500-800 miles doesn't amount to a $20 bill. Normally at least 80% of my miles are interstate or cruise-controllable roads. Only way to pick up ANY mileage without cruise is if you're pittlin' along going up grades and ain't worth it in my book.

Imo, the issue is the 5.3 makes torque at higher rpms than the good ole 350/5.7. That one had lots more bottom grunt. Axle ratio makes a difference but still relates to rpm torque range. Mine has 3.42 ratio. If I could get my non-towing highway mileage while pulling the boat - now THAT would be something...But I can't justify a diesel just to pull the boat

[MichPhoenix77]

I have an '06 and pretty much same. I make a couple long trips south each season. I've done various scenarios to experiment and concluded, leave in tow/haul - set cruise - and let'r eat. The difference over the course of 500-800 miles doesn't amount to a $20 bill. Normally at least 80% of my miles are interstate or cruise-controllable roads. Only way to pick up ANY mileage without cruise is if you're pittlin' along going up grades and ain't worth it in my book.

Imo, the issue is the 5.3 makes torque at higher rpms than the good ole 350/5.7. That one had lots more bottom grunt. Axle ratio makes a difference but still relates to rpm torque range. Mine has 3.42 ratio. If I could get my non-towing highway mileage while pulling the boat - now THAT would be something...But I can't justify a diesel just to pull the boat

This!

I also have a 2004 Silverado with the 5.3. I set the cruise and tow haul and go.

[Dave A]

I have the same truck with the Z71 package, extend cab with 373 gears, I've tired it all and settled on pulling it down in 3rd and let her roll. My manual says to use tow haul if your pulling 75% or more of the GVW, my bass boat doesn't come close to that. Using 87 octane i get between 11&12 mpg. When I bought my truck I asked the mechanic and he said don't tow in overdrive.

[TiGer85SS]

These trucks need 4.10 gears if you are doing any type of towing. Your mileage won’t really be affected that bad because the engine will be working more efficiently. I just finished doing an install on my 05 Silverado.