I finally had an hour up at the dock to take a look at the thermostat housing so see if there was any blockages. Sure enough, the bypass passage had 2 pieces of old impeller stuck fast in it. It took me a whole 2 minutes to remove the housing and a half hour poking and prodding the 2 bits out and 5 minutes to get it all back together again. Fired it up and within a minute or two, the temp started to come up, it now runs at an indicated 170-175deg. I'll be changing out the impeller that is currently working fine next weekend as preventative maintenance. I would have done it but I didn't have a socket extension long enough to clear the retaining bracket in front of the seawater pump. So, anyone with a VP V6 or small block v8 should take a look see in the housing if they are running into a problem with not coming up to operating temp.