96 LT1, 101K miles, Auto

My car started overheating the other day in stop and go traffic, I pulled
over into a car wash and sprayed water on the radiator and it started to
cool down.  It got up about 234 degrees.  The last two years it starts to
overheat on real hot days and in stop and go traffic.  I'm thinking I need
my radiator swapped out.

But, my question is after it cooled down and I noticed that it was kind'a
shaking at traffic lights.  Then today on the way home my Service Engine
Soon came on.  AutoZone read the code and they said it P1153 and that it was
a dealer code that they would have to check.  Their equipment didn't go that
high???  Wondering if anybody has any ideas on what might be my problem.  I
don't have any oil in the water and no water in my oil.

Any advice will be appreciated.

Thanks,
RP