engine light PO138 code

From : john begin

Q: hi gang i have a 1998 ram 4x4 with 90000km. the truck is automatic and has a 318 engine. the check engine light came on and i took it in and was told that it had a 02 sensor downstream shorted to voltage. they got the light out but it came back on 2kms down the road. it is code number 138. i am also getting my gearshift vibrating badly just sometimes around highway speed.if you just touch it stops so i dont think there is a lot of pressure causing the vibration. had all wheels balanced and universals checked. any help would be appreciated thanks john .