GMC 2005 T-Series Owner's Manual page 52

Six-Speed Transmission
The transmission has gears that automatically
synchronize when you shift up or down. Choose the
gear which will maintain the road speed you want while
keeping the engine above two-thirds of the governed
speed. When the engine speed drops below two-thirds of
the governed speed, shift into the next lower gear before
your engine begins to become sluggish. When you shift
down, be sure to double-clutch if required.
See "Double Clutching" later in this section.
® ®
Eaton Fuller Nine and Ten-Speed
Non-Synchronized Manual
Transmissions
If your vehicle has one of these non-synchronized
transmissions, it is naturally somewhat complicated. The
label above the windshield will tell you the operating
basics you need to know.
The following are driving tips:
•
Always choose an initial starting gear suitable for
the load and terrain.
•
Always use double-clutching procedures when
shifting.
2-18
•
Never move the range shift lever to the LO speed
gear position after HI range preselection, or
anytime the transmission is in the HI range.
•
Never move the range knob or lever with the shift
lever in NEUTRAL while the vehicle is moving.
•
Never make a range shift while moving in
REVERSE (R).
Double-Clutching
You must use the double-clutching method when you
shift an unsynchronized gear set. Disengage the clutch,
shift to neutral and engage the clutch. When upshifting,
slow the engine until the engine rpm and road speed
match. When downshifting, accelerate the engine
until the engine rpm and road speed match. Then
quickly disengage the clutch and move the shift lever to
the next gear position and engage the clutch.