Form Slow, Then Fast

I have a very puzzling situation with a database. It's an Access 2000 mdb
with a SQL 7 back end, with forms bound using ODBC linked tables. At our
remote location (accessed via a T1 line) the time it took to go to a record
was very slow. The go to mechanism was a box that the user typed the index
value into a combo box, with very simple code attached:

with me.RecordsetClone
.FindFirst "[Index] = " & me.cboGoTo
If Not .NoMatch Then
Me.Bookmark = .Bookmark
End If
end with

Now, one would say that going to a record is slow because I'm using
..FindFirst over a T1 line. And that's what I thought. However, as I was
working with the form, commenting out various sections not related to the Go
To, I found that the Go To functionality changed, though I didn't modify the
code.

Previously, going to a record near the end of the 50,000 record recordset
took about 1-2 seconds, but going to a record near the beginning, took about
20 seconds. After the form changed, going to any record in the recordset
took about 1-2 seconds.

So the question remains: why did it take so long to go to a record near the
beginning of the recordset, but not near the end (and the ones in the middle
took an amount of time about halfway between the two), and what changed so
that now the form is working fine for all records?

I've compared the changed form with the previous copy, and I don't see any
differences. I've compared all code in the form module, and I've compared
all form properties. The forms are identical as far as I could tell. But
something happened as I was commenting/uncommenting code in the form that
got rid of the problem with it taking a long time to go to some of the
records.

My first thought was that something got recompiled, and now the form is
fast. So I went back to the original version and changed some code and
recompiled, also did a compact and repair. But it was still slow. I also
tried doing an explicit decompile and then recompiled it. But it was still
slow.

So this is very frustrating that the form is now working fine, but I can't
see anything that's changed. If I don't see why the form is now fast, then
there's no reason to believe that it might not at some point go back to
being slow again. And then I'd just have to hope that something changes. It
would be good to figure this out.

Any ideas as to what might have changed here to cause the form's Go To to be
fast would be appreciated.

Thanks,

Neil