Would it not be worth buying a basket case truck with a good drive line and swapping this all over?
You would get all of the small components that always make a swap more expensive and difficult.
Or do you need/want to stay with the 8 bolt?
As for your current engine/ gearbox set up I would have thought that it would be able to navigate hills with ease if it was all in fine health.
Have you run a compression test?
Are you sure you have full throttle?
Is the timing set correctly?
Exhaust blocked?
Always a good idea to check the basics, I spent weeks chasing a misfire only to find out that it was one of the new plugs I had fitted but, of course, it couldn't be the plugs as I have just changed them....
P.
