Noticed the ATS reading on the scan master runs over 100 on hot days ambients about 90-95. If setting it goes over range quick and driving around town I am seeing 125-130 ATS. Would a cold air kit help? Water temps run 200-218 with stock cooling system..
@ that eng temp, the rad is rejecting some serious BTU's into the under hood air. I think this is where some of your hi IAT's are coming from.
I did some testing on my 55/LS set up, as I was seeing some similar readings. I instrumented the under hood area next to the filter, put 1 in ft of the core support.
@95* ambient, 190* eng temp, I was getting 130+ IAT's. [the same as under hood temps.] The PCM was pulling timing.
I built an air box w/ a thru the core support inlet, and put the filter in the box. The box is insulated on the inner surfaces with Dynamat material.
The IAT's dropped to ambient, while moving. As I stopped in traffic, it rose some 10*, but never got to under hood [130*+], temps.
I use the Fluke meter I got from Percy's. A 2 station unit with k thermocouples. The IAT's were read from my laptop thru EFILIVE. [IAT sensor is in the MAF.]
Works for me..

Will be doing the same on the T Type/LS turbo set up. The main difference will be the turbo will be connected directly to the box., and be fed from the pass side headlite area, and the inner fender where the batt was.The inlet is 5".