Engine strange acceleration
 

So I have a 1999 4.3 Jimmy Blazer with 99.419 miles and manual transmission.
It runs perfect except for one thing, acceleration. When I'm driving and step on the clutch or put it on neutral, it randomly revs all the way up to 2.000 rpm and keeps there until I bring it to a full stop. It happens randomly but mainly when engine it's hot.
I noticed that it's also backfiring and seems to be running rich.
From my researches it seems like a bad rotation sensor but I'm not sure of it.
Any of you guys had a similar problem?

Thanks in advance.