my tranny is not shifting, I think it's in limp mode. other problems which started at the same time, are tach and speedo aren't working, shifter indicator light is out and engine light is on. when scanned nothing came up, but got much worse today. Was suggested by one guy that it is my ignition switch, any thoughts on this? tumbler or whole assembly?

should add that it's a 96 6.5

I would go at the ign switch for sure. These trucks are very well known for having these problems. The switch feeds everything you mentioned having trouble with. I would also carefully check all the fuses. Use a testlight on each side of the fuse, dont rely on a visual inspection as sometimes that will bite ya.

tumbler or whole assembly?Plazzman - the ignition switch and the lock cylinder are two separate animals...What you're looking for is the ignition switch...starts by the lock cylinder with a long harness down the steering column where it is plugged in at the bottom of the steering column...It will probably set you back about $150 for the part.....the gm part number should be 26036311

Check the trans fuse first. If no power there most likely it's the ign switch like the others have said.

please explain your shifting problem more. how is it acting?