4L60E Transmission problems

I have a 97 GMC Sierra with a 4L60E transmission. Recently it started acting like the transmission would not shift right. It starts out fine but when it gets to about 30 MPH the engine revs up but the transmission does not do anything. It acts like the torque converter loses torque. When i slow down it kicks back in. I was told that sometimes you can change the ignion switch and fix this. Anyone know anything about this problem.

Yes the ign swtiches were problematic in this year but only a trans scan will reveal if this is the problem, no power to the internal solenoids, any other symptoms, no CEL, or other systems not working?

As far as I can tell everything else is fine. There is no service engine light on or anything.