I've always found hard/abrupt shifts to be vacuum related.

One thing you might want to pursue is simplifying the vacuum system: first by converting to a pressure wastegate, thereby eliminating all the vacuum stuff on the passenger side; then by other odds and ends.

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 159k miles
06 E320 CDI "Rutherford", Black on Tan, 179k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 145k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 77k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife