Nissan Repair: 1995 Nisson 4x4 pickup, gas mileage, 5th gear

Question
I have developed a noticable vibration when shifting into 5th gear. All other gears seem to be OK. No problem shifting between gears. Goes into 4x4 OK. Had u-joint & drive line checked...they are OK. Only have 122,000 on the vehicle. Have any ideas? Don't drive in 5th...am afraid to worsen the problem. I am a grandma and want to be well informed b/4 I find someone to check it out! Hard to find fairness and integrity. My son, who does not live close, feels it might be the bushing/bearing for 5th gear and maybe it can be replaced instead of pulling the transmission. Figured you know your business and could help me make an informed decision. Thanx

Answer
Barbara,

Is the vibration when you are driving slowly in fifth?  If so, you need to be going faster like fifty or better and if going up a hill you need to downshift into fourth.  Overdrive is only for gas mileage.  If you lug the engine it will eventually blow fifth.  Now, if I am full of it and this is not the case and it only vibrates in fifth at any speed and in all conditions then you might look at the motor mount on the back of the transmission and the back u joint again.  Lastly, it could be the bearings but it is doubtful for only fifth.