1999 Gmc Sierra 4.3l Performance And Fuel Econ

lubben810 · May 1, 2011

Alright let me start out by saying I love my truck. Its a 4x4 reg cab long box. Not super common. For what its used for, it works very well. However me being human, Im looking for a little more. At highway speeds(65-75mph) It will barely maintain speed, and most of the time Im pushing the pedal down almost to the point to where its downshifting. Even light grade hills are an enemy. The only load it hauls is my dirtbikes, which is 600lbs on the high end. NOT exactly a impressive load, however even that makes the highway unenjoyable. I have replaced the fuel filter, plugs, wires, distributor, ect. So far no significant changes. Also, for a V6, it dosent seem to get the best fuel economy, I would assume since it takes so much gas to get it going. Are there any quick fixes, or simple hop-ups to this motor to wake it up. Ive considered a cold-air intake and throttle body spacer, but Im wondering what can be done before I stick $$$$ into it. Im not looking for a race car, but if Im going to drive a V6, it had better be able to pull 600lbs down a highway and get better fuel economy than the small V8's. Fill me with your guidance and knowledge!!!

CapitalTruck · May 1, 2011

75 is going to be pushing it for that engine/body/4wd layout, not matter how much you goose it. You have a nice truck there for working bulky cargo, even in limited traction conditions. It will never be a highway cruiser. Slow down to 60 and take it easy.

dsr611 · May 2, 2011

Im not looking for a race car, but if Im going to drive a V6, it had better be able to pull 600lbs down a highway and get better fuel economy than the small V8's. Fill me with your guidance and knowledge!!!

I traded my 98 Sierra Ext Cab last year for my '10 Sierra crew cab. The 98 had the 4.3L V6. I got the V6 thinking that it would get better mileage also. My dad had a 97 Sierra Ext cab, and he always got better mileage than I did. The only loads I ever pulled with my 98 and my dad's 97 was our 4wheelers. When pulling it with my 98, I could tell that the trailer was behind the truck. I couldn't tell it was behind the truck when pulling it with my dad's 97.

When I got the 98, I got the V6 thinking it would save on mileage a little, but it didn't. Think of it this way...with 2 identical trucks, one with a V6, the other with a V8...in the truck with the V6, the engine has to work a little harder to do the same work that the V8 would do. That alone is going to cause mileage to go down.

rgv · May 2, 2011

what gears and tires are you runnning?

I had a 1995 K1500 with 5-spd, 3.73's, stock sized 245/75/16's and it had no trouble maintaining speed and pulling hills with moderate loads in the bed.

That truck would go 800 km (500 miles) on a tank in town easily.

blacksierra01 · May 2, 2011

My 2001 4.3 reg. cab long box is exactly the same, so are all the ones we have where i work. They all have 3.73 gears, and for a v-6 i think they are terrible on fuel. The same truck with a 4.8 gets better milage. I wouldnt waste my money on any performance upgrades, just save up for a v-8, thats what i'm doing.

Stevens03 · May 3, 2011

If it was me, I'd put a cold air intake on it cause I believe they help and look into a custom tune. If that wasn't enough, I'd look into the gearing and possibly swap out for a nice set of 4.10's.