How does your truck drive? I feel like mine is way down on power, well below where it should be. Empty, it still wheezes up relatively steep hills in 2nd gear and takes forever to grind up to speed on the highway. With ~1000 pounds of logs in the bed, it needed 1st gear to grind up a hill at 20 MPH. Although I know it's only a small-block pulling 6000 pounds of truck (mine is the heaviest of all, 4x4, extended cab, long bed, 8800 GVW), it seems like a turd, even with 4.10 gears. It doesn't much like to rev, either.

I don't believe it is the plenum. I've looked down the throttle body and it's dry in there.

I also only get about 10 MPG, empty or hauling a load. I don't expect more than 15, but 10 seems kind of low for an empty truck. I've got it tuned up as well as I can with plugs, cap, wires, rotor, coil, new O2s, new distributor, etc., and it runs smoothly. It's just dog slow and struggles to pull large loads.

I'm thinking perhaps the cat is dying, but it seems to blow clean. It's just less powerful than I think it should be. I've got an exhaust leak under there anyway, so I'm going to replace the Y-pipe and cat. I know it's a heavy truck anddon't expect it to be even moderately fast, but I'm wondering if it is under-performing. It just feels puny.

Is this normal or what?

 

what size tires are you running, when i went to 35's my power vanished, that is why I am going with 4.88s

 

death flash? On your PCM does it have sticker saying authorized update?

 

It could very well be a cat starting to clog.This will give you your loss of power,and poor gas mileage.And the revving problem is another indication.

Get it flow tested.It may not be bad enough to kick a code,but on it's way.

 

same deal with me. im thinkin its my gears, 4.10's pushin 35's might be hard on her. im thinkin 4.88's would be alot better. its a bitch drivin to the mountains, gotta floor it to get the tranny to downshift and get up the hill.

 

i find mine to be a terd as well. ive done the t-stat the tps mod. i run synthetic oil and a few other things and it made a difference but not what i expect from this size motor. my ford 5.4 would out tow this motor no problem. dont get me wrong i love my truck but for a 5.9 i expect far more. im looking into the round air cleaner as well as a hypertech tuner. prob a fastman tb. and a dual exhaust with headers. if this doesnt do the job well i dont know what else to do.

 

I'm running 265/75/16 tires. Big, but not huge. No death flash sticker, though that doesn't mean it hasn't been flashed. We'll see what happens after the new cat.

Given that we're all thinking the same thing,maybe it's just a very puny engine in a giant truck. A small block just isn't enough, and 340 pounds of torque from 360 cubic inches is a joke. Hell, the 2.7L V6 in my allroad makes 388 with a chip. Even at 4200 pounds, that thing moves like a Mustang.

I guess it's slow and thirsty and unreliable, but it still hauls everything I throw at it. Next timemaybe I'll go diesel, though. Thanks for the responses, guys.

 

i think your cat is clogged, because my truck acted worse with a clogged cat. when i got it changed out it ran like a bat out of hell.

i wouldnt say they are unreliable, my motor is running very strong, has good pickup for the weight of the truck, and it does a decent job of towing. Im currently looking and saving for a wrecked 12 valve that i can do the swap over once fuel prices, come down, if ever.

fix the minor problems with it and it will be a beast again.