I'm asking for a friend so I'll give you all the info he gave me.

Vehicle is a

78 dodge d150
318
2 wheel drive
Automatic
Regular cab
8ft bed

And heres his question

I want to replace the 727 with a good overdrive like the 518? (i think that's it) any suggestions on this? I need something non computer controlled and strong enough not to blow up if I'm hauling a bed of mulch or drywall lol. The build purpose of this truck is to use it as a truck and to cruise...my days of racing are done with...i just want better gas mileage and reliability.

I am absolutely clueless on this, and the only thing that popped in my head was "If you could just put a different factory trans in place of a 727 why would so many people buy gear vendors overdrives?

So any help is appreciated.