Chevrolet Repair: 1996 1500 4.3 vortec rough idle, trans tech, deceased father

Question
Recently accquired this truck from my deceased father and cannot figure out why it won't idle well. Have checked all known sensors and changed fuel pump. It's supposed to get 66 psi and gets close to it. The only thing I can figure, is it needs the old gas drained and refilled. Used to need starting fluid to start, now it will start and run ok at regular driving speeds (except transmission won't shift into 3rd gear - submitting to trans. tech).

Answer
Hi Matt... if it's been sitting for a time a good fuel cond. would help, or some good inj cleaner.. if rough idle continues try some air intake cleaner thru the breather...also check the EGR and idle air control...both could need service...hope this helps