davester

the site still works for me. likely your isp is a problem. It's also possible that your region has been blocked by that forum due to a lot of spammers (I have no idea where you are located).

And depending on what year the vehicle is, there isn't much of a fuel filter in the system, so particles will wind up clogging the injectors. The very early GMT800's (up to around '02/'03) had a return fuel system, with an inline fuel filter that did a good job of filtering, but later trucks use a really poor "filter" as part of the in-tank fuel pump. After getting a bunch of crap in my fuel tank, and subsequently having to clean my fuel lines and injectors because of it, I put in the inline filter used in the earlier trucks, and haven't had a problem with it since (but also haven't had any extra crud in the fuel either).

I would suggest putting on the parking brake, chocking the wheels, then putting it in drive, making sure the vehicle isn't going to move forward, then start testing power and ground at the bulb connector, then working back.

Well, you have to take the interior panel off to lube everything, so when it was off, did you try just flipping the lock by hand (ie, the lever at the end of the rod going to the interior lock switch)? If the rod moves freely, and the switch doesn't, then (assuming the rod isn't bent or moved out of it's guides) the door latch unit is busted. It's not that hard to replace.

Then we've been turning a corner every day for the past 8 months? The normal use of "turning a corner" means something significant/noticeable has happened recently that changed the situation. Nothing significant has happened, particularly w.r.t. the 3 things you mentioned, anytime recently.

If you are eventually going to swap in a Duramax, I would suggest getting the 11.5 inch rear end. While the 10.5 will likely work fine most of the time, do you really want the rear end to blow up again sometime when you get on the go-pedal with the Duramax, particularly with the big tires and higher ratio. It sounds like this is a vehicle you want to keep and use for some time, that would be another reason to not try to save a few pennies up front...

From what I've read, GM and Eaton don't specify adding friction modifier to the gear lube for G80's, and that works for most people, but some people find it chatters a bit sometimes for them, and adding a bit of friction modifier makes that go away, and it still works properly.

Maybe -look at the knock sensors electrical output with an oscilloscope -look in the cylinders with scope via the spark plug, and with it up the intake and exhaust to get a look at the valve seats

If, in 4wd, you can't rotate the lifted wheel but you aren't getting any power to the front wheels, then something isn't fully engaging. There is no clutch to slip. You might re-verify the front axle actuator extends about 1" or so, when you are trying to hold it back with your hand and someone shifts the truck into 4wd, to make sure it does fully extend under some pressure. If you are certain you aren't getting power to the front wheels in 4wd, then I would suggest splitting the front diff or pulling it, and then checking out the front axle locking setup (locking gear, passenger side stub axle, other stub coming out of the diff on the passenger side). Then, if all those look good, then it's crack open the transfer case to check it out.

Have you considered reading the owners manual to see what it says about that feature?

Put the truck in 4wd and lift up one of the front wheels. Reach under the truck and try rotating the front driveshaft. If you can rotate the driveshaft, then something is wrong with the transfer case, broken chain, shift fork problem, gear problem. If the driveshaft doesn't rotate, try spinning the lifted wheel. If the wheel doesn't spin, you are in 4wd mode. If it does spin, and you've already verified that the actuator pin goes in/out as you shift in/out of 4wd, then bits in the front axle are busted. The locking ring (this is what the actuator moves to lock the front axle) or the passenger side stub axle are common points of failure in this case.

Sure, new parts can be bad, right out of the box. But, you say that directly providing power and ground to the pump turns it on. If that's true, then you have a electrical problem. I would find a connector that's fairly easy to access & unplug, that has the wires that eventually go to the fuel pump, and apply power and ground directly to the pins in the connector, and see if the pump works or not. Then go closer to the pump if it doesn't work, or further away from the pump if it does.

When I did the pumps on my truck, I compared the tops of my existing pumps with new ones on rockauto, so it had the same number and orientation of connectors on top. I have a cab&chassis with a wood deck that I can pull up the boards to have a look and work on them, so it was easy for me to look at them. You might be able to reach up with your phone and take some pics or a video of the pump from underneath the truck...

The electrical/computer stuff changed a lot in '03/'04 range, as well as the fuel system (switched from a return system to a returnless system.

From the description for that product, it is not a fuel filter, but rather an oil filter setup... That said, lots of guys go for third party fuel filter setups for their Duramax's. They like clean, water-free fuel...