95 SLS Transimission issue

You had only one shift solenoid replaced, there are two. Your description of the symptom, is it just no fourth gear? Does it reach a point that all you get is engine speed increase, and no power like slipping? When you let off the throttle at cruise, does it coast or the engine drops to an idle, and applying the throttle is void until you reach the point the the car accelerates? Is there a check engine light on?

Can't guarantee at this point, if the second solenoid is at fault. It would take knowing which of the two(A or B) was replaced. On the early models of 4T80E, the filter in between the solenoids would push out and eventually break one of the solenoids. A new solenoid kit would include two solenoids, and a bracket with longer bolt to prevent this from reoccurring. You can press off and warmer on your climate panel with the key on, it will display powertrain codes for you, as well as other modules codes if any. Record the powertrain codes and report back.