davester

You've checked ALL the fuses, including the ones in the end of the dash by the driver's door.

Common things that can fail, and kill mpg but may or may not turn on the cel, are -fuel pump failing (can't maintain full pressure)->test fuel pressure on the rail both at idle and when you speed the engine up to say 2 or 3k rpm. -exhaust manifold bolts break off (causes exhaust leak, which screws up the O2 sensor readings so they read lean, and the computer starts dumping in fuel) Replace bolts (which can be a hassle) or get exhaust manifold clamps for the end bolts (particularly useful for the 2 rear bolts), and perhaps even replace the exhaust gasket as well.

With my '04 Sierra (with a completely different wiring & computer setup from yours), my backup lights (and a couple other things) wouldn't work when a fuse to the bcm had blown. You might check all the fuses, there might one that isn't obviously for the backup lights, but still affects their functionality.

year old thread, and the o.p. hasn't returned since around it was started, so you guys are unlikely to get an update/outcome...

you may need to indicate which specific vehicle you want this visor for. But, I can't help you with finding one...

Yes, the truck has a socket, that you can plug a third party TBC into.

I wouldn't expect an '02 harness to work, as GM rejigged the computers for the 03 or 04 model year, which changed a lot of stuff.

You know it's good because "US WAREHOUSE - HIGHER QUALITY THAN OUR COMPETITORS"...evidently, storing a China product in a US Warehouse somehow makes the product better...

Yeah, you want to use a DexIII fluid. DexVI is supposed to be backwards compatible with it, but at least for some transmissions/transfer cases, they leak after switching. If the unit has been rebuilt since it was manufactured (and after around '06-'07), then the seals likely have been upgraded to work with DexVI. For my truck (which has a '06 transmission & transfer case now), I put DexVI in the transmission, but DexIII in the transfer case...

That's funny. There are a whole bunch of electronic components that have to work right, for even your key ignition vehicle to run, for most vehicles made in the last 20 years or more. And what is the key ignition the "backup" for, that a push-button start wouldn't be?

From several forums where there have been threads on this, most people find "plain" 75W90 works fine, some people, for whatever reason, find the G80 chatters with using plain, and adding a bit of friction modifier makes it go away. GM claims the G80 doesn't need it, I believe some people have found Eaton (who makes the G80) does want the friction modifier (as it does have a clutch).

... and there's not much in the parking brakes to make a clunk, short of some part having come loose to roll around inside. If you can't hear a loud clunk doing that test with the engine spinning the wheels, maybe try repeating it, and use a mechanics stethoscope (carefully) to listen to the backside of each hub, and to the diff housing, maybe you can hear something using it.

Maybe chock the front wheels and using the engine to spin the rear wheels. If you know it has an open diff and not a G80, you might also chock one rear wheel and then other other and see if it happens on one particular side (If you have a G80, this is dangerous, as when the relative speed difference makes the G80 lock, then the chocked wheel will suddenly really want to spin).

I would expect them to be largely the same, as GM only made relatively minor improvements to the truck over those years, but I don't know what those differences are. If you want to be sure, you might get the paper version (I bought it myself for my '04 sierra, I didn't want to be using a computer while working on my truck), and then get an online subscription to the fsm for the right year, to get the differences, the subscription is pretty cheap (<$50 for 5 years).

a wiring and/or connector issue?