I changed my spark plugs but my chevy still idles funny and in reverse it acts like it wants to cut off

 

We'd need a bit more information about that.

What Blazer?
Model?
Year?
Engine and engine type?

What exactly is "idles funny"?

Is it doing this only in reverse, or as soon as it is put into gear?

When related to spark plugs always check:

- Are all connectors properly put into place?
- Is the firing order correct? (cables put where they should go?)
- Do one or more spark wires arc? (May check in the dark - No touching thou!)