I have never heard of that happening to a Chrysler motor before.....A friend of mine has had it happen to two GM trucks he has had, though. The first was an early '90s GMC Sierra 1500 with the 4.3 V6. He was towing a trailer, not accelerating but rather just cruising along with it and the engine started shaking and losing power like you described. He called me and we looked it over. There was no compression in the number two cylinder, so we pulled the head and found a big hole in the piston. Also as you said, no bent valve spring or broken valves. The other was a late '80s Chevy van that the same friend and his band bought to haul their equipment. Again, no warning, and then the engine went. And again, no apparent valvetrain breakage. I wonder what causes things like this to happen spontaneously like that?