could be misfires or possible torque converter shudder in lock up. best to visit your gmc dealer
Check motor mounts
Braking
Your truck may not shift gears because the transmission sensor is damaged or broken. It also may not shift gears because the transmission or linkage is damaged.
Whichever is lighter will accelerate more quickly.
The larger (and therefore heavier) the vehicle, the more gears are required to accelerate it. Larger engines such as the ones in transport trucks also have much lower RPM limits, so they can not be revved nearly as high. A typical accelerating truck generally revs between 1700 and 2500 RPM. This very short range means far more gears are necessary to permit the truck to accelerate or climb hills. Without a lot of gears (sometimes as many as 18 or more), the effect would be very similar to trying to start a passenger car from a full stop in 4th gear - i.e: the engine just doesn't have enough power at excessively low RPM.
My truck flutter and temperture gauge drop at the same time
your accelerator is finished (broken)* basically you don't have an accelerate, just two brakes :3
Well if you have a carberator on this truck it is most likely the booster pump
it has both chain and gears
COULD BE A NUMBER OF THINGS...YOUR POWER STEERING PUMP MAY BE BAD.
an automatic transmission shifts through the 4 or 5 gears for you as you accelerate. a manual transmission must be shifted by hand using a shifter and a clutch (located next to the left of the brake pad).
Your transmission is in need of servicing.