Transmission shift indicator light out=no upshift

hi, l have a real problem here,my 96 gmc seaira 4x4 has developed a shift indicator light flicker and now is totaly out.
When this happens l have no speedometer or rpm gauges working so then l have no upshift as it is controlled by the speed .
Now the light does come on once in a while and then its back to normal with all gauges and upshifting working , when its out ,l have none.
HELP ANYONE ,thanks

ignition switch is probably shot

Nope Jeromy had that checked , what else could it be anyone

check for power on the trans fuse when your dash goes out, if there's 12V on that wire check the round plug on your transmission case to make sure it is properly seated, no wires are backed out or contacts dirty or corroded, and put some dielectric grease on it. Also check the trans fuse to insure proper contact. The white wire from the ignition harness feeds the trans fuse, after the trans fuse it is 2 pink wires, one going to post e on the transmission connector(transmissions only 12V source) and the other pink goes to the instrument cluster. There is a TSB covering this problem on 97 and newer trucks with the 4L60e transmission but it seems to happen even on any truck with the 4L60e(93 and newer) in it. Take a look at this post http://forums.pickuptruck.com/showflat.php?Cat=&Number=309973&page=0&view=collapsed&sb=5&o=&fpart=1
Your SES should come on when the trans doesn't shift with codes P0740, P0753, P0758, P0785, and P1860