Car Will Not Shift Into Overdrive, Runs Rough/Dies When Put Into Gear

Hello All,

I have a 1987 Cadillac Brougham, which will not shift into overdrive.  It also dies when
initially putting into gear, unless I step on the gas.  After it gets going, and I stop, it just
seems to run rough when stopped in gear.  Runs smooth when idling in P & N, and at
all other speeds in gear.

I know it's getting old, and the overdrive gear gets worn over time, but I'm wondering if
this has to do with the transmission sensor?  Maybe something else?  It is throwing a
code, but I haven't checked it yet, and don't know if it's related to this issue.

Hoping to avoid a tranny rebuild... I think wishful thinking is better than not thinking!!!!