Could someone please help,

My '98 Sentra Si 1600 suddenly quit revving past 2000.

No matter if I'm in park, neutrual, or in any gear.  It is absolutely
fine
until it hits that mark and then all of a sudden it begins to slowly
die and I cannot accelerate (no warning signs appear on the
dashboard),
like it isn't receiving any more fuel.

If I push my clutch in and the revs drop back below the 2000 rpm line
the car continues to run. This problem occurs randomly and without
warning at times which makes it harder to diagnose.

I have checked/changed the following:

-Tested Fuel pump relay and check fuel
-Press check and clean distributor cap
-Rotor treat against moisture check
-Power to fuel pump - took fuel sample
-Checked for water in fuel

Also, I was thinking alternator - but the battery light would be on if
this was the case?

If not that the computer, or something causing the computer to
malfunction as its misreading it/supplying false information?

These problems just started and any info would be greatly appreciated.
I thought it might be important to mention it was rainy weather when
this happened. I dont have much experience with cars :( Im still quite
young and this is the first vehicle I've owned. So please..If its not
too much of an inconvenience would you mind explaining in lamens
terms :D sorry.

Thanks in advance.