Any faster way to loop through the item record sublist and set values? It takes so long using current record

nlapiSetLineItemValue in combination with nlapiRefreshLineItems

by long do you mean lots of code, or lots of time or both?

Lots of time. The whole screen pauses for like 3 sec for it to loop through the list and set ship dates.

I think you are doing this on a client script, there is a flag related to async commit, something like that, I do not remember well, but depending on the value, it will be faster each commit line. Check the docs.

There is the ignoreRecalc option but that doesn't seem to do much

is this a client script?

Yes it is

are you using 'dynamic mode' to access the lines? if so, perhaps try standard mode?