Why would there be occasional abrupt engine missing in a 1994 Suburban 350 that is getting worse and occurs when the engine is warm but nothing shows up when dealer tested it?

Well the first 2 things I would check would be the plugs and do a cooling system pressure check. These engines will loose a head gasket if the coolant system hasn't been maintained well and the hotter the engine the worse the leak. The big reason for this diagnosis is the dealer will only check (eletionic issues) most of the time when (any engine problem occures). The one other thing that comes to mind is the intake beeing loose. Some times these engines (even after miles and miles of good service) the bolts will come loose and eventually suck in parts of the intake gasket. ( I've seen this atleast a dozen times). hope this helps you out ... good luck