Strange starting issue

Cheapest thing to check and not a bad thing to change is your fuel filter. (especially on a new engine) I am wondering if it is getting a little plugged and it is taking that little bit of extra time to get the fuel pressure up enough to start the car. Try keeping your key on for a few seconds before cranking it over and see if it starts.

Next thing I would check is your timing. You may be a little off on it, and that will definitely make the engine turn over a little slow. Although this doesn't usually happen until it is warmed up.

If you think it really is the slow crank causing this, make sure all of your ground wires are clean and connected properly. Also check the cables from the battery. My 86 had slow crank issues and once I changed the battery cables, voila no more problems. (about $20 fix saved tons of head ache) Take your battery up to autozone or something and get it tested to make sure it is good as well.

I agree with the other thoughts. Re-test things, starting with the fuel pressure . Lots can happen during an install - chunks of paper towels get left in lines, etc.

Just for consistency, I would add a 4 gauge motor-to-body ground strap at some point.

And just to clarify, it cranks just fine but won't catch till you let off the key and try to start it a second time, right?

Oh, you were the one with the paper towel. We've all done it.

If you have a FP gauge, you might as well toss it on and see what's going on while the pump is doing its thing.