How to use INDEX and MATCH to replace VLOOKUP?

I've got a workbook with 700,000 cells. It uses VLOOKUP in about 110,000 of these cells. This causes the workbook to slow down so much that it almost hangs.

So I want to replace VLOOKUP with INDEX and MATCH, on the theory that this will use less CPU/Memory.

I've tried to create a replacement formula using these functions but it is giving me an #N/A.

I've attached a (small) sample workbook which contains my non-working formula, as well as the original VLOOKUP formulas which do work correctly so that you can see what I'm trying to accomplish.

Any advice? Thanks!

How about
=IFERROR(IF(O36="","",INDEX($M$36:$M37,MATCH(D36,$D$36:$D36,0))),"")

Thanks Fluff, that worked! Looks like I had switched the arrays?

You're welcome & thanks for the feedback
The match function can only work on a single row or column

OK thank you!

My pleasure