2000 5.3 195k fires perfectly when cold, and perfectly after roughly 10 minutes of driving/stopping/restarting. After 20 minutes or so, and then after up to 6 hours of sitting, will not fire until roughly 3-5 seconds on the starter.
For what it's worth: new plugs, wires, and fuel filter eight months ago. New alternator, battery, and belt last month; new tps two weeks ago to no avail.

Any help would be greatly appreciated, thanks in advance.