water flow problem
 

new engines , coolers , etc. one engine has less water flow than other other enigines have 3psi at 1500rpm but one only fluctuates between 0 and 1psi , I took cap off of thermostat housing water flow is visably less than other engines .
changes water pumps to rule that out no difference
next I am going to try to backflush from pump thru drive to see if there is a problem there anyone have any thoughts ???

Could be a restriction in the transom assembly. Hook a hose directly to the water pump inlet and see what happens. The fittings in the transom assemblies are notorious for narrowing over time. Check this and go from there.