As earlier said, I checked the connections on my Coleman 550 on Friday 12/12, and I believe mystery is solved. The starter is definitely kaput, but the fault lies with me. Upon examining - cleaning connections, I discovered a second ground connection at the starter, in addition to the ground connection on the frame. The battery connection and wire for this second ground had fallen through the opening in the battery compartment and was just laying loose below the compartment out of site. I believe this happened in my haste to replace the original battery with the O'Reilly battery and the OVERSIGHT continued with the installation of the second "higher cca" Interstate battery and the new solenoid.
My continuing to start the UTV with a sluggish starter by jumping the battery or using a higher CCA battery burned the starter out. The starter was not getting enough voltage to it without that 2nd ground. This happened to me once before with a tractor starter, but I guess I didn't learn. I was desperate to keep the utv going feeding cattle, now we're feeding with the pickup and an extra hand.
The UTV is in the shop getting a new starter. Thanks for all the imput!