Spent the holidays changing fluids in the truck. Did the diffs (GL5, LSD in back, used the additive), coolant, transmission (GL4), and transfer case (same as the tranny). Has 170K miles, and don't have any repair history, so I thought this would be a good idea. No problems except the transmission, which is now very stiff to shift in 1st & 2nd gear. No problems before changing fluid, it looked really black and nasty. Just a little fuzz around the drain plug magnet.

I used GL4 (read on the forum many times to make sure it was GL4), but couldn't find any viscosity numbers on it (not the normal 80-90W type of numbers). It was the only stuff I could find. It just said GL4 140. Is that my problem? Is it too thick? Seems to get better as the truck warms up. Any help would be appreciated. I can certainly change it again, just be out a few dollars.

You pegged it, Frby98.

Dump that goo and get some
MT-90 REdline( GL-4), either locally or online- it's 75W90- what you want. brace yourself at checkout.

overfill it quart and a half more over the fill plug to keep bearings/seals alive in the trans.

X2 what Bille said. Worth every penny.
Believe it or not, an oil that is too slipppery will not allow the synchros to synchronize the gears quickly enough to avoid grinding and such. You see, the synchro acts like a brake of sorts. A thick, 140 weight oil is too much of a film for the synchros. It improves with warmth because the oil gets thinner.

If you live in a moderate to cold climate, go with RedLine MTL. It is a bit thinner than the MT-90.

Here's what to do until you can change the fluid to a lighter weight.

Start the truck and let the truck warm up 10-15 minutes. The warmth from the engine will warm up the tranny and the fluid inside it. Will allow you to shift a little smoother until you can change the fluid.

Considering it's really cold outside right now I would switch to a lighter weight of fluid asap.

that's what I was afraid of. oh well, it wasn't too hard to change.

However, I keep hearing about overfilling through the shifter. I'm a little intimidated in taking that apart. Any advice? Before, I just lifted the driver's side and tilted the truck, got in about 1 qt extra.

Also, should I change the transfer case also?

Filling through the shifter hole isn't bad, as long as you don't spill it inside the truck

Let me clarify my request - does anyone have some instructions on getting into the transmission from the top? I searched this forum and didn't find anything.

TAke the trim off around the shifter.

Unbolt the shifter plate on top of the trans. Watch for the spring when you take it off. It won't go flying or nothin, just don't want to lose it.

REassemble after filling up. Use gasket maker of choice on the shifter plate.