Making more sense now, it seems your IAT is likely to be accurate and is down to lack of airflow.
A shroud is vital for the SMIC otherwise airflow will flow around the cooler rather than through it (path of least resistance), especially if airflow from the rear of the cooler is restricted.
Unless there is visible damage to the core (blocked fins) then stripping the pipework won't achieve anything. Either work to improve airflow or a Front mounted Intercooler to suit your choice of bumper is needed.