Thanks for the suggestions. I will have to look into those jets. I already tried adjusting the idle mixture screw, but it won't turn, and if I remember right, the slot is the worse for at least one attempt prior to mine.
I am in central WY, and got the truck just before a spate of sub-0 temperatures. When this hit, it would not start because the hoses to the HAC valve were all disconnected and hanging loose. I plugged those leaks and it started, but not willingly. Now, after setting the timing, slow idle, and fast idle, it runs and idles a lot better but the starting hasn't improved greatly.
I love block heaters. But this is a field truck that needs to start in all weather, even if I don't have an outlet nearby.