Hey guys got a couple questions. 1984 F250 6.9 bored to 7.3 4x4 4spd reverse over and down. Don't have a tach in it.

First question . Yes I've drove a manual before. What speeds do I shift for best fuel economy?

Axle code is a ...P what gear ratio would be best for that. 3.73?

And how fast should i run in 4x4 high and lo.?

 

As quickly as you can without stalling the engine.

There is no axle code P, that is a transmission code for a t19 4 speed

As fast as you would like, the engine is governed to 3300 rpm.

 

You can decode your certification label here and figure out the axle ratio: Certification Label - Gary's Garagemahal