backfiring, finding TDC

[Guardrail]

I suspect the firing order got messed up along the way and is now beginning on the wrong cylinder. I thought your motor would have a crank snout bolt to use to turn the engine, but you can turn the engine without one.

You can remove all the spark plugs so the engine is much easier to turn. Put on a pair of gloves so you can get a good grip and use the alternator belt to turn the engine. If you are standing in front of the truck looking at the engine, you'll want to go clockwise.

Cylinder number one is on the drivers side front of the engine and number two is directly across from it on the passenger side, and so on. You will need cylinder number one at TDC on the compression stroke and I'm assuming you know what to look for to make sure you get it there. Once your there, pop the distributor cap off and mark where the rotor is pointing (it's now pointing to cylinder number one). Then go thru and check the firing order. I suspect you'll find the problem now. Let me know how it turns out....