1990 gmc 4.3 tbi auto, 102,000mi Sometimes has rough idle at stoplight, and when warmed up shudders or stumbles when I step on the gas both from a stop and when driving in town or highway. No codes. New fuel pump(delco) and filter w/in 10,000mi, cap,rotor,plugs and wires w/in last 25,000mi. Tested converter(according to youtube video) and is good. Found and fixed a vac leak, but didn't help. Any ideas on what to do next? Thanks