So my husband and I just picked up a 92 GMC 1500 4.3L. So far we've done an oil change, new fuel filter and air filter. It seemed she was running strong at this point. As a precaution, we did a tune-up and reset the timing. Now she sputters and dies or is extremely sluggish with the pedal to the floor. We are at a loss as to what could be causing this.

 

One thing I've learned when troubleshooting a problem is to determine if anything has been changed lately. I would go back through the tuneup you did and relook at the timing and check all wires for breaks and make sure they are on the right plug. On a truck this old the wires and vacuum hoses may be brittle and break easily. Easy to break something and not know it. Good luck and let us know what you find.