I wanted to make a few comments here:

One is about the idle. Unlike the Subaru you have Jim,we tiico owners have a harder time with the idle. At least mine with the high output engine is controlled by the map and ecu.You can adjust a little with the throttle cable. Any playing with the timing is a big no no with these motors to turn up the idle. Jealous of you subie guys on many aspects...hindsight is 20/20 on that one.
Another problem I noticed with the several tiico I have seen is they hot test the motors and that leaves the coolant internals full of rust by the time they get there. That could be start of your radiator getting clogged. I also wonder if when most people switch from the waterboxer to the I-4 they stop using phosphate(sp?) free coolant. Says in the install directions of the tiico to use regular coolant. This may cause some corrosion in aluminum parts that were "used" to the phosphate(how do you spell that word??) free stuff.
I think a good start like Terry pointed out would be the radiator. I would pull it and flush it.
Have you done anywork and reversed the hoses going to the radiator? I would also check your thermostat and make sure it opening fully.
If for any reason you want to pressure test the system, I have the adapter/tester I can send you if you want to borrow it.
Bill

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