99 GMC Suburban 2500

I have a 4L80E Transmission in my 99 GM Suburban which has decided to start a new life of its own. PROBLEM: Leaking, will not engage reverse, Neutral is confident it wants to now be in drive or 3rd! Could the problem be coming from the sensor or perhaps from the linkage as well? In drive the trany goes through the gears well, just no (R). Thanks to all gearheads for suggestive input.

Welcome to AF. Usually caused by the reaction sun shell and shaft splines stripping, quite common, it has to come apart for repairs. BTW, in the Chev section we have a dedicated Suburban forum, for your future posts.