I've been experiencing the same problem. I also cleaned and lubed the cylinder and it worked better for a few months. I am wondering if it is the key more than the cylinder. Did the dealer cut new keys from your existing key. If so, the old key might be worn out and new keys cut from it will have the same characteristics. Can the dealer cut new keys or order new keys with just the cylinder number? This would ensure a good new key with no worn defects.

Ryan
95 T100 2WD ExtCab
All Stock