Trouble code "transmission module unstable". on 1998 GMC Sonoma

code checker used shows a code "1870" trans module unstable, have cleared it several times, comes on after 40-75 miles. What are possible fixes? Where is transmission module?

Asked by for the 1998 GMC Sonoma
stop clearing the code and take it to a shop so they can see the freeze frame data to help them determine the problem. unless you have a scan too that can acess the info for the trans, throwing parts at it can be very expensive.