1989 Isuzu Trooper Hesitation Problem

Hello I have a 1989 Isuzu Trooper 2.6 4ZE1 four-cylinder engine. I was recently having start-up and acceleration problems while changing gears, so yesterday I replaced the Fuel Pump,Fuel Filter and Spark Plugs.The hesitation stopped for a day, but now im having trouble when i try and crank it,and as i shift into 1st and 2nd gear it hesitate and sometimes stall, so i have to idle the engine for a few seconds or so then its fine, but if the engine is off for 20-30 minutes or more,the same thing happens.
Please Help,