Its possible it could be the shift module on the actual shifter inside the car, Those go bad and will do exactly what you said yours is doing. You will need a mechanic with a scan tool able to test that part. I know SNAP-ON tools sells those special scanners for about 5K so you wont find them in every shop.

__________________
Live simply so others can simply live



07 E350 sport Wife's Daily
01 E320 sport My Daily
00 C230 Kompressor Our back up (new Arrival)

87 300D Turbo my Daily for 8 yrs. Selling to neighbor

82 GMC Jimmy (K5) 6.2 Diesel (my Wheeler)
73 Roadrunner 340ci My very first car, still own it