W126 72235 transmission: when put in D transmission shifts perfect 1-2 shift but when it goes to 3rd it spins; when placed in 3 it shifts perfect one shift ten spins next shift; P-R-2 engagements are smooth and w/o problem. Recently installed a new modulator valve no improvement in symptoms but made transmission shift even smoother. Review of threads suggests that it could be adjustable b1 piston; or plastic b2 piston bad; bad governor; front pump. Which is most likely the problem and can it be fixed with transmission in car? I would appreciate any suggestions.
Karl