Then on my way home I lost power then stalled?

My truck was running fine, except for a leak in the exhaust manifold only when cold, until one day on my way to work I started losing power a little bit. Then on my way home I lost power so bad I couldn't get out of third gear and exhaust was blowing out of the exhaust manifold big time. Now I have fixed the exhaust manifold, replaced timing chain and sprockets, changed spark plugs and wires, changed thermostat and done almost every diagnostic test in the book and now I am stumped