I have a saved search for an item fulfillment. I need to join information on the item sublist of the fulfillment from the item sublist of the sales order. Is there a way to get only the sublist line of the sales order that are associated with the sublist lines of the fufillment without getting tons of extra data?

depending on which direction you are starting from, use the applied to transaction or applying transaction join

@Azi

var vendorpaymentSearchObj = search.create({
type: "vendorpayment",
filters: [
[
"type", "anyof", "VendPymt"
],
"AND",
[
"custbody_9997_pfa_record", "anyof", context.newRecord.id
],
"AND",
[
"mainline", "is", "F"
]
],
columns: [
search.createColumn({ name: "currency", summary: "GROUP", join:"appliedtotransaction", label: "Currency" }),
search.createColumn({ name: "creditfxamount", summary: "GROUP",join:"appliedtotransaction",  label: "Amount (Foreign Currency)" }),
search.createColumn({ name: "formulacurrency", summary: "SUM", formula: "{appliedtotransaction.creditfxamount}*{appliedtotransaction.exchangerate}", label: "Amount (Bank Currency)" }),
search.createColumn({ name: "statusref", summary: "GROUP", join:"appliedtotransaction", label: "Status" })
]
})

the general idea is in these searches you can do joins, in this case i'm getting Bill level information on a Bill Payment search The joins work both ways, so I'd create a transaction search with these fields and joins and figure out what you need