GM-GMC: truck stalls under load, spark plug wires, gmc sonoma

Question
My friend has an 92 GMC Sonoma V-6 5 speed 4 wheel drive P.U. It runs real good at idle,and at 1/4 of gas pedal pushed down. When he tried to pull up a hill he has to go to a lower gear and only use 1/4 gas pedal. When he give it half pedal it will cut out real bad and not pull. It will even cut out on a level freeway if he gives it more than 1/4 pedal. He has changed plugs. Any idea what he should try next? Thanks for your help.
Gerald

Answer
Try changing the spark plug wires, distributor cap, and rotor.

Also, be sure that the air filter is clean.  Change the fuel filter if it has not recently been changed.

Most problems like this are ignition related, so the spark plug wires and distributor parts should be changed first.