Help please, Im stumped.

[NuBomb]

My 91 Silverado with a 350 is doing something very similar. It idles fine when cold, but once it warms up, it idles like it's ready to die. I've done many of the things you mentioned including taking it to a shop because it after idling so low, the oil pressure light kept coming on. I took the throttle body off and cleaned it real good, did a tune up, checked for leaks, replaced egr gasket, replaced coil, replaced filters and nothing. The truck showed no codes at the shop and I can't keep paying for someone else to chase the problem. A buddy of mine suggested I have the catalytic converter checked. I guess that is next. I'll be checking your post since it looks like we may have the same problem.