low power when hot?

I did set the valve lash cold when I was going through everything (per @pishta 's recommendations on a previous thread) so even if its off, it shouldnt been that far out of whack but I'll go back and set it hot in the near future. Also - given that this is a 2ish rebuild engine and I'm skeptical about the integrity of the last one, a burnt valve isn't out of the question. However, how would that not show itself at every temp or every RPM? The good news is I have another head that seems to be in good shape so worst case I can swap it.

I've checked the heat riser before but I'll do some more intensive testing with the heat cycles. Worst case, Would it be the end of the world to get it stuck in its "warm" position or remove it? cold starts aren't much of "cold" starts in Georgia and even then its in the garage.