Thank you all for responding,
I have tried to open the gas cap before I try to start it, there is a very small amount of vacuum present when I open the cap, but it does not help with starting. I have also looked at the manual shut off lever, it is in the full upright position when I try to start it. Is it still possible that there is still some vacuum pressure preventing the valve from functioning properly?

The cranking speed seems to be the same when hot as it is when cold.

Could this be a timing issue? Either timing chain (I have not checked the stretch) or the pump timing?

One more thing, sorry such a long post, but this may be important. There is a greasecar system installed that I have never used. It was installed by the previous owner, but I have been spending my time trying to get it running properly before I messed with that. I have heard of the greasecar switching valves sticking in various positions, should I plumb the fuel system as original and see if that makes a difference?

Thanks again!

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1987 300TDT ~264,000 miles