w140 trans problem
 

Previous owner claims transmission was rebuild by Lee Miles transmission shop with OEM MB parts last year. Transmission engages harsh from P to D and soft from P to R. It slips or flares when upshifting into 4th gear when cold. When warm 2nd to 3rd shift feels firmer than 3rd to 4th shift. And I also hear howling sound in N and when accelerating. When I release gas and just roll howling noise goes away. It seems like transmission either was never rebuild (they just tweeked modulator pressure) or rebuild poorly. What do you guys think? Is there anything I can check? Or shall I take car back to a shop and what do I tell them? K2 clutch is slipping? Pressure incorrect? Bad front pump?
Car is 92 500sel with 150k ml.
Thank you