looking to make my truck motor and trans reliable

[dead civic]

Hi, I have a 79 truck

with a 350motor/trans combo.
I want to be able to drive the car form California to Oregon. but my motor shuts off at random times, and the transmission leak fluid from some part that i till today I don't know what it's called.

what are my options?
buy a motor and trans combo that i can just drop in, where would I buyt this from?

or should I rip out the motor and trans and rebuild it? I

I'm highly interested in a transmission that will have a nice low RPM on the high way. what trans should I look into.


sorry for the run on paragraph any information is greatly appreciated, thanks.