Igition module and tach.

I have a 98 ZR2 4.3 TBI.I'm still trying to figure out this problem I have.When the truck warms up,while driving down the road.The tach will jump up and down and then die completely.While the tach is jumping around the engine runs like shit and damn near dies.As soon as the tach quits the engine runs somewhat fine again.Once truck is parked and cools down for a bit the tach will work again and so the process starts all over again.I have heard that it could be the igition module.So what I want to know is that if there is a connection between the igition module and the tach?It would make sense.

$66.00 later and the igition module didn't help.