pitman arm won't fit

[Lady sparkie]

I have tried 3 different manufacturers (NAPA, Moog, and GM Certified part) for my 2003 chev. silverado. Went into dealership to return part that won't fit-new part has identical part # as is on my truck, but is approx. 1/16th to 1/8th of inch too small on lower spline. All parts tried were too small. Chev. dealer said that all pitman arms made from 2001-2006 have the same stock #.

 

They want me to put into their service department and pay them to tell me what gear box or spline part is on my truck. Help!! Is this possibly a Canadian part or some other chev. make part??