my 3 and 4 went out and it was the band inside the trans died and messed the clutch pack drum out. Did you install a Corvette servo or a longer 3-4 engage pin? I tried the solenoid tests per an ATSM before replacing them and mine tested good. I finally broke down and yanked the trans apart to find the dead band. What killed mine was 0% torque management banging the gears from 2nd to 3rd.