One problem related to noises during shifting has been reported for the 2001 GMC Sierra. The most recently reported issues are listed below.
Engine uses to much oil, knocks, smokes body- truck bed sides are rippeling because the metal is to thin,& can not handel the weight of a lumber rack, front bumper is dented on both sides but in differant places, was like this at delivery, all the trucks were like this but all of them in differant places. Manufacture defect exhaust- loose parts inside of muffler, exhaust rattels from mounting hardware, muffler retains water and leaks at the seams. Paint-rust on the top of cab seatbelt- driver side belt will not recoil,broken seat belt bracket. (this is a safty issue) tires-below 1/32 tread left at 23,000 miles(this is also a safty issue) transmission-makes a cluncking noise at low speeds,takes a long time to shift when running the a/c also makes a howling noise,transmission slips.