GMC 1996 Sierra Owner's Manual page 82

If your speed drops below 20 mph (32 km/h), or if the
engine is not running smoothly, you should downshift to
the next lower gear. You may have to downshift two or
more gears to keep the engine running smoothly or for
good performance.
If you have a five-speed manual transmission with low
gear (RPO MW3), the following charts show when to
shift to the next higher gear for best fuel economy.
Acceleration Shift Speeds
VIN Code 2 to 3 3 to 4
4.3L V6 (W)
15 mph 40 mph
(24
km/h)
(64 km/h)
Cruise Shift Speeds
4 to 5
SO mph
(80 km/h)
4.3L V6 (W) 15 rnph 25-40 mph
45-SO mph
(24 h d h ) (40-64
k d h ) (72-80
km/h)
Shift Light
SHIFT
If you have a manual
transmission, you may have
a SHIFT light. This light
will show you when to shift
to the next higher gear for
best fuel economy.
When this light comes
on,
you can shift to the next
higher gear if weather, road and traffic conditions let
you.
For the best fuel economy, accelerate slowly and
shift when the light comes on.
While you accelerate,
it
is normal for the light to go
on and off if you quickly change the position of the
accelerator. Ignore the SHIFT light when you downshift.
If your vehicle has four-wheel drive and is equipped
with a manual transmission, disregard the SHIFT light
when the transfer case is in 4L.
2-20