1983 Ford Ranger Engine Jerks while driving

I have a 1983 ford ranger that has 170,000 miles; but it has an engine from a 4.0L engine out of a 1996 ranger with 40,000 miles. Out of no where my truck just started to Buck & Jerk while driving, at times it lacks power. Rangers have an in-tank and an in-line fuel pump. I replaced the in-tank fuel pump and it's doing better, but it's still acting up about 4 or 5 times everytime I drive it. Any suggestions?
-Thanks, Jacob