I recently purchased a 2003 Chevy Express 3500.

I need to add fluid to the rear end but depending on if the differential is locking or not the fluid spec is more restricted.

Also -

Can anyone describe the viscosity of the fluid that is supposed to be back there. I'm horrified by how thick the stuff is on the plug ... as if it is graphite putty ... please make it not be metal dust.

 

I dont know the weight but it supposed to be thick. I dont even know if there is a specific difference. I had a Mercury Grand Marquis that required 80-90W but when I was doing it when I was working at Chrysler they didnt have that weight they only had 75-140W so that is what I had to use.