I was having some of the same problems with my ride. Running a 50/50 mix with new alum. radiator with A/C on. Pull off the interstate into heavy traffic in August and the heat would build. The people who built my radiator said the thing is good for a lot more ponies than my L6 is making. I noticed my aftermarket radiator cap was getting corrosion on it. Got a "water-wetter" as it has anti-corrosive stuff in it. The antifreeze mix is 25/75 with a quart of this "water-wetter" in it. The heating problem has gone away. No more than a 5 deg. swing in any traffic condition. Don't know what fixed it...the ratio mix or the "water-wetter".
