Mark,

1. Verify that its actually running at 225 degrees with an IR
thermometer. Point it and shoot to get the actual temp.

2. If its really that high :  wash the radiator/condensor surfaces real
well.

3. Seal up all sides of above.

4.  See if your lower radiator hose is collapsing at higher rpms.

5. Thoroughly clean your cooling system with Prestone H.D. Cleaner. ANd,
open all block drains for flushing out.

6. Run no more than 25% antifreeze in the summer , because water is the
best coolant. (add more antifreeze for winter if it gets below 20 f
where you are).

7. If your water pump is the original, id think about a high capacity
Stewart Brand pump . Im very impressed with them. Thier website has an
Open Forum for overheating problems with a qualified Tech answering
questions.

8.  For kicks, you could take out your thermostat , temporarily, to see
how it runs .

On my 85 it cycles between 228 and 210. The computer is controlling the main
fan.

Is it constantly at 225?

If this only happens with a.c. on on my 85 there is a small fan in front of
the condenser. Do you have that too? If so it cycles on air cond head
pressure and as emergency fan if block temp gets over preset number like
240. This sensor is located between plugs on the passenger side.

Have you tried water wetter? Adding it to your radiator is supposed to
reduce the running temp. It's available at most any chain auto parts store.
Brad