what is life expectancy of a tow bar

I've had 2 Blue Ox bars and get mine checked/serviced annually at Quartzsite, however, I've replaced them at about 70,000 even with the professional service. The connecting knuckles and all swinging joints are wearing way too fast in my opinion. On both bars I've had to disassemble and put steel shim stock in the bolt holes to compensate for wear. I've also had to replace one set of toad connecting knuckles due to tow bar wear. I recently purchased a Road Master Blackhawk 2 and have no intention of going back to the Blue Ox's.

We pull the Silverado but load it to 6500-7500 pounds for summer Alaska trips and Arizona snowbird trips, which should be well within the weight limits Blue Ox specifies. To me they just wear too fast