One pipe steam system issue

The pipe leading up to the system is cool half way to the system.

What do you mean by "system" here?

The problem is likely a pitch issue with the pipe for that radiator holding back the steam

Does it eventually get hot on a very long call for heat? Do you ever hear any gurgling from that radiator?

that is odd. The next thing I would try would be to close the valves on many of the other radiators and try a long call for heat

You may have a main vent that has failed or the system is not producing enough steam.

How is the boiler fired? If it's gas fired you may not be getting enough gas at the boiler. Several years ago ,y system did not seem to be working right and after hearong some neighbors complaining I checked my gas pressure and found it was dropping to just over 2PSI under load. The gas company replaced the incoming gas line (the 80 year old pipe was filled with rust, and the pressure was fine after that.

Clock the gas meter and make sure it's burning gas at the correct rate -

"Look for the smallest test dial on the meter. Get a stop watch. Get the single piece of equipment you want to clock running. Everything else should be shut off, don't worry about pilots on other equipment. If for instance the test dial you are using is the 1/2 foot dial let it make two rotations (makes the math easier) It becomes the same as a 1 foot dial. So lets say it took 20 seconds to make two rotations of the half foot dial. You divide 20 into 3600 (number of seconds in an hour). In this case 20 divided into 3600 is 180, what is 180 it is 180 cubic feet to then find BTU's multiply 180 times the Heat Value of a cubic foot of gas in your area or if you don't know use 1,000 which means the equipment you clocked is burning 180,000 BTU's per hour. This should closely match what is on the rating plate of the equipment listed as INPUT.There are charts and tables for all of this in NFPA 54 National Fuel Gas Code. There is also a procedure for altitudes in NFPA 54."

Bob