Hi, Steve. I can believe what they are telling you. Back in the 60's, many homes were built with 60 Amp service to the whole house. And we know that most plugs are for 15 Amp service max. But there is one other factor at work. Over the years, pine will harden. I had some plywood from the 50's and could not believe how hard it was to cut.
Remember, though, that this is not the fault of the saw. It's doing what it was advertised to do. It's like buying a sand blaster and hooking it up to a small compressor. When the compressor runs out of air, it's not the sand blasters fault that the compressor did not have enough capacity. You have to either stick to tools that use less air than the compressors max output or buy another compressor. P-C answer was really telling you to use a lower capacity tool. You could start asking the homeowners what amp service they had in their house and turning down those with 60 amps. But how many homeowners know the answer to the question anyway?