I have a 98 GMC 4x4 and it shifts up and down while driving under 60 mph and it want do it running over 60 but it runs and shifts fine whats wrong?

Electronic Module on the side of the transmission it's like a brain it's kind of all about six inches long and about 4 inches by 6 inches wide it's electronic computer is the computer for the transmission but it bolts to the side of it goes to the shipper that one note on it that holds the shifter rod on anyway it's all most likely it's probably probably needs another one of those it should be on the driver under the driver's door facing facing that side but it's be on the side of the transmission it's black in the and it's like I said the shifter rod goes on it and a black nut goes on it but it's got a number like a clock clock counterclockwise or clockwise and most likely is bad because I had wondered the same thing shipped down by itself most likely that's what's going to bethanks David Bigcountry Wardlaw, Bigcountryonlineproductsangoolelplaystore Bigcountry American pide