Pintle hook mismatch
Bob, was the truck/trailer combination on uneven ground? CMP trailers had lunette eyes that were able to swivel to allow for rough ground (and fixed, except for slop in the spring mounts, tow hooks). The US standard was the other way around, fixed lunette and swiveling hook. Just for fun, did you measure the ID of the CMP tow eyes compared to the US standard to see how different the fit is? I know that when I towed the red frame around with my 10,000 pound rated hook the fit was quite loose. The CMP hook has always struck me as oversized for its rated load.
Normally people think of the problems of having both able to swivel (the whole hitch can end up upside down) but with a reasonably close fit between hook and eye to reduce slop in the hookup, uneven ground can cause binding. To avoid this most modern pintle setups (at laeast the light weight ones) have some built in slop and as a result, some people criticize them for being a rough tow.
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