4l60 slipping

I have a 94 z71 with a 4l60e. in manual it drives fine in first or 2nd, In drive or overdrive 1st and 2nd seem fine but at about 3 grand in 2nd the engine just revs like in neutral and If I slow down a little it never catches untill i stop then it starts over again. I was wondering if that means anything in perticular maybe shift solenoid. I read an old post where a guy had a similar but not exact problem and said it was the ingnition switch does anyone know anything about that?

Check fluid level and fluid condition and filter.
Get it on a good transmission capable scanner and check for codes and see if any thing shows up.
Post back any codes.

Check fluid level and fluid condition and filter.

By this MT means drop the pan, drain the fluids and see how much debris is at the bottom of the pan and in the filter.

If it's very dirty, there is a good chance that you have found the source, or at least a contributing factor to your problems.

I have found that about a third of all shifting/slipping problems have been fixed with a fluid and filter change, and a good pan clean -out. So since the pan is off already, install a new filter, put the pan back on, fill with clean fluid and see if the problem is still there

The 4l60e transmission has shift patters controlled by the PCM. If there is any shift solenoid problem the PCM will set a CEL and if failure requires the transmission will go into limp home mode "SECOND GEAR TAKE OF IN DRIVE" or harsh shift pattern by increase of line pressure. The problem you described most likely is caused by mechanical failure in transmission. An inspection of the transmission pan will reveal this to you after a scan for transmission codes. If you have codes I can give you the possible causes and repair for problem.