Have a 2000 Silverado. The transmission has a RPM fluctuation between 45 and 55 mph. Wondering if anyone out there has had this problem or if anyone has any ideas as to what this might be. Torque converter or maybe electrical? Only happens in overdrive.

 

mine is an 03 and i have the exact same problem...it has been in the shop a few times and no ones seems to think that is a big problem...let me know if u hear anything about it please