One problem related to noises during shifting has been reported for the 1999 GMC Jimmy. The most recently reported issues are listed below.
The 4l60e transmission seems to be running hot during warmer summer weather & while driving up hills towing a trailer. The transmission also seems to be shifting rough during warmer summer months too. There is a shudder every once in a while during low speed turning. Now there is a noise consistent with a speed around 55 mph.