I have an AMC Eagle 1981 with the 258HP AWD.Question:  Have T-5 manual trans in my Eagle, Runs well in the first 4 gears, but in 5th have a vibration under load. Any ideas?Answer:   It is possible the 5th gear set in your T5 manual transmission is starting to pit.  When this happens it can cause a vibration like you are describing. 5th gear is the highway gear obviously so before condemning the transmission we would suggest you have the u-joints, drive shaft all checked and balanced and also check tires and balance. This may not be a trans problem at all but associated with the transmission. We believe in elimination of the easy potential problems before tearing into the transmission.Need additional technical support give Scott a call 888-824-2012 he can help you.