I have a issue with shifting into 4th gear. Occasionally it would not go into 4 gear, but now it seldom with go into 4th. When it does, the transmission works perfect. However when it fails, not only does it not go into 4th, but if you stop, it fails to return to 1st. It seems to be stuck in 3rd gear. Now, if you shut off the ignition, it returns to 1st and goes to 3rd normally, it just never goes to 4th. To complicate matters, if you put the gear shift in 3rd (not D), you don't have the issue with it not returning to 1st when stopped. Obviously, it has no chance to going to 4th with this shifting choice.

 

Have you had the codes pulled?