The Stovebolt Site Forums The Parking Lot Big Bolts engine swap

I can understand wanting to run the 454 and turbo 400 you have. Making that choice you are accepting the limitations of that combination.

If you look around you'll find 1-ton pickups, weighing about the same as your 6400, pulling 5th wheel trailers, and running the 454/turbo 400. Talk to the people using them to get a sense of how well they do. These will be older trucks because most now have an overdrive automatic like the 4L80e.

Using a 6000 pound 454 powered pickup to pull a loaded flat bed car hauler weighing 7500 pounds I was able to exceed the freeway speed limit, and climb my own steep driveway. (I say was because that truck was totaled in November.) Remember the 6400 moved the load with a 235, but did not do so at speed.

You've defined more of what you intend to do. I'd suggest thinking in terms of axles both front and rear from trucks that weigh at least 6000 pounds and are rated to pull the 5th wheel trailer. Choose a rear axle ratio used in a big gas powered Chevy or GMC pickup designed to pull a 5th wheel.

Most of what you are trying to do has been done by General Motors. Look at their solutions and ask users if they are satisfied with how they work. Then copy the ones you like best.