2004 AWD trans fluid and filter change help

hello all,
i'm donating my labor for a friend's 130k mile AWD exhibiting a intermitten shudder that feels like low ATF fluid only when going up steep inclines (i have yet to check fluid level). in any case, with the OEM fill still in, i plan on doing a filter and fluid change.

GM parts tells me the filter comes with the pan gasket, but beyond that i wanted to know what else to anticipate. is there a drain plug on the pan- need a o-ring replaced?
for fluid replacement i wanted to do the running exchange- disconnect cooler line and while vehicle running, add equal amount to fill till fluid color changes. is there a line easily available to disconnect?

tia,
parker

The shudder could be from the transfer case. It may be time to change the AutoTrak II fluid.

I wouldn't bother with the trying to flush the oil cooler. There is probably no drain plug, but it would be a good time to install one. The trans linkage bracket will likely have to be removed, then the pan can be removed. Replace the filter, use the original pan gasket if possible, and clean the magnet in the bottom of the pan. Make sure the filter pickup tube seal is intact or replace it with the seal in the filter kit.

Changing the 5-6 quarts in the pan and the filter should be adequate to fortify the oil enough to prevent problems. If the trans oil has never been changed, plan on doing it again in 7,500 miles then return to the recommended 30,000 mile change interval.

blue bowtie, thank you. it was a long day but its been at least a couple hundred miles and going. no shudder reported.

update: shudder has returned. now occuring at easier inclines than before. i will change the transfer case oil and report further.

At that mileage, it's well past due. Don't try anything but the OEM AutoTrak II oil.

update. i feel that the trans fluid change has created a bigger problem. ran perfectly for 1k miles after the fluid/ filter change but now the vehicle shudders- feels like it's studdering between driving/ forward motion and neutral. only noticable in 1st and 2nd gears. fluid smells burnt.

give it to me gently- did i buy a new transmission?

the transfer case fluid was replaced as well, but the driver says there was no driveability change.