Need Help Please

[94MellowYellow]

Hello, I have been having a problem where at start up and up until the car is warm maybe after about 10 miles or so there is a lack of power, a loud rumbling sound around the transmission area, the stick shift vibrates a lot, and when driving, the rpm needle will hesitate, then after about 10 miles or so, the car will run fine, very frustrating, none of the local mechanics have any idea of what is going on, I will appreciate any help, thanks and I am happy to be a new member