Are all 6 running the same IOS version? Also I had a similar problem with 2 switches and I update the IOS to the latest on just one and it fixed the CPU problem, your IOS seems quite old, might be worth updating on just one of them.
First of all, your switch is not 3550. 3550 is not XL series, your switches are 3548XL.
Your IOS is affected by the bug regarding high-cpu utilization for "Router AutoConf Process" (Bug ID: CSCdv21552). Though from the "show proc cpu" there is no indication that your high-cpu utilization is cause by this bug, if you have an active maintenance, it will not hurt to update the IOS.
I noticed that you put "spanning-tree portfast" in all if not most of your physical interfaces. Make sure that non of them is connected to a hub, switch, or routers - otherwise you will create a network loop and will cause high-cpu utilization. "spanning-tree portfast" setting for the physical interface is recommended only if the interface is connected to a host.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...