Running into Portal Report performance issues upgrading from 17.3 to 18.4

Hi All,

We are upgrading from 17.3 to 18.4 and we are observing a behavior in Appian, with the same amount of the portal report data there is jump from 75 sec(17.3) to 102 sec(18.4). 

The report is implemented to format the portal report data into an array of CDT, so that CDT array will be used to further do the paging and sorting on the Grid. we are currently hitting 2600 rows of data from the portal report and using a!foreach to do the formatting the rows into CDT. 

I appreciate if you anyone has an idea why there is a jump in the processing time? 

Is there anything we can leverage from the parallel processing aspect of 18.4 here to improve the performance.  Is a!forEach function evaluate the rows parallel or in Sequential?

thank you for all the support

Malavika