A couple of comments...

1. Don't substitute Summing for Retrieval, unless there are no duplicate
records. If "no duplicate records" qualification holds...

=VLOOKUP(C44,'Sheet1'!$C$13:$AA$3000,25,FALSE)

should be mapped onto a SumIf formula, not onto a single-condition
SumProduct formula:

=SUMIF(Sheet1!$C$13:$C$300,C44,Sheet1!$AA$3000)

Under such benign conditions, SumIf might fire better.

2. If you can sort C13:AA3000 on column C in ascending order and
maintain the area sorted...

=IF(LOOKUP(C4,Sheet1!$C$13:$C$3000)=C4,
LOOKUP(C4,Sheet1!$C$13:$C$3000,Sheet1!$AA$13:$AA$3 000),
"")

will be enjoyably faster.

SteveC wrote:
=VLOOKUP(C44,'Sheet1'!$C$13:$AA$3000,25,FALSE)


=SUMPRODUCT(--($D13='Sheet1'!$D$13:$D$3000),'Sheet1!AA$13:AA$300 0)