Before you get into any more second guessing take the truck out and run it down the road for a bit, getting it fully up to operating temperature and running it easy through the rpm range - no need to see 5000rpm or more, but run it up & down, exercising the engine a bit. Then come back and see if the lifters are still clicking. If so then I'd let it cool down and go through them again, being 100% sure that you're starting on #1 compression, both valves closed and off the lifters, and proceed through your firing order getting the pre-load right. If they still click then think about going to see your supplier. Just my $0.02....