ignition problem comes and goes

my 1993 with 5.7l will run fine for about 30-40 miles, then all of a sudden
it will run very rough with the RPM gauge jumping up and down, stalling and idling very poorly. After stalling, it will start right back up, but run poorly.

I shut it off, removed the ignition module,(which is new) from under the distributor cap, re-install it, and the truck starts up, idles fine and drives home with out any problems.

I've done this twice with the same results...

Any Ideas on what could be causing this?

my 1993 with 5.7l will run fine for about 30-40 miles, then all of a sudden
it will run very rough with the RPM gauge jumping up and down, stalling and idling very poorly. After stalling, it will start right back up, but run poorly.

I shut it off, removed the ignition module,(which is new) from under the distributor cap, re-install it, and the truck starts up, idles fine and drives home with out any problems.

I've done this twice with the same results...

Any Ideas on what could be causing this?

Check the distributor and the plugs and plug wires first. The distributor could be messed up, or it could be the firing order is off or improperly gapped spark plugs.
Then check to see if there's a blockage in the fuel system.
Then check the timing, it may be that it's jumped time.

thanks for the reply, and I hope your right...
I change the plugs, wires, cap and rotor with the same results.
I hooked up the timing light and faced it to the cab, then I started the truck. Every time It would sputter it looked like it was losing spark.
So, today while it was running it's worst, I shut it off and changed the distributor, started it and set the timing and it seems to be running fine.

I'll post after I test run it for a while...

Sounds like the ignition module may be failing when it gets hot. Then when you take it off and put it back on, it cools down to the point to function correctly again.

have you had anymore problems from the truck?

My truck is still running great, the small round piece under the rotor was loose and seem to be causing my problem. But, all is good now.