328 Auto Transmission: will not shift to third

Help anyone. I've got a 96 328 with auto trans. Lately the shift from second to third gear has been slow to engage. Yesterday, third gear would not engage at all. From the moment I started the car, 3rd was gone. 1st and 2nd shifted just fine but 3rd never fully engages. Drove it a little today using different variations on the shifter. Got it to the point where 1st, 2nd 3rd worked but at highter rpm's. Now the Electronic Transmission Control Module (ETCM) trouble code lights on the dash. Does anyone have any idea? It feels electrical. Is the ETCM a unit that can go out and cause this type of problem? Is the ETCM an easy fix or does it require internal work on the Trans? Thanks for your help.

im not really sure what it is, but i would try checking the tranny fluid. also smell it and feel its consistency to see if it needs to be replaced