GMC 2006 Sierra - Manual (Page 446)

Check the fluid level only when your engine is off, the
vehicle is parked on a level place, and the transmission
is cool enough for you to rest your fingers on the
transmission case.
Then, follow these steps:
1. Remove the filler plug.
2. Check that the lubricant level is up to the bottom of
the filler plug hole.
3. If the fluid level is good, install the plug and be sure
it is fully seated. If the fluid level is low, add more
fluid as described in the next steps.
How to Add Manual Transmission Fluid
Here is how to add fluid. Refer to the Maintenance
Schedule to determine what kind of fluid to use. See
Recommended Fluids and Lubricants (Gasoline Engine)
on page 6-14.
1. Remove the filler plug.
2. Add fluid at the filler plug hole. Add only enough
fluid to bring the fluid level up to the bottom of the
filler plug hole.
3. Install the filler plug. Be sure the plug is fully
seated.
Hydraulic Clutch
The hydraulic clutch linkage in your vehicle is
self-adjusting. The clutch master cylinder reservoir
is filled with hydraulic clutch fluid.
It is not necessary to regularly check clutch fluid unless
you suspect there is a leak in the system. Adding fluid will
not correct a leak.
A fluid loss in this system could indicate a problem.
Have the system inspected and repaired.
5-speed for VORTEC™ 4300 V6 and 4800 V8 engines
shown, other manual transmissions similar
5-34