sputters between 1st&2nd gear

I Have 96 Astro &have Had A Jacobs Electronic System On For 1 Yr. Recently It Started To Sputter Between 1st&2nd Gear.replaced Cap ,roter,wires,&fuel Filter.problem Stopped For A Month,started Up Again,somtimes Wouldnt Start.suspected It Was The Jacobs.disconected It.ran Fine For Couple Of Months ,problem Started Up Again&cut Out On Highway.had It Towed Mechanic.fuel Pump Coms On But Low Pressure.replaced Fuel Pump[ouch!].starts Fine But Have Same Problem ,sputtering Between1st&2nd Gear Hot Or Cold .can Anyone Advise Me ?