95 blazer/jimmy running issues

i have a 95 jimmy/blazer with the cpi motor in it. the motor has 101,000 on it. the truck runs fine except if you baby the throttle and watch the rpms around 1500 to 3000 it will bounce around if under slight load. but you can punch it and the truck seems fine. also when accelerating 3/4 or less until the motor hits 3,000 it seems dead. like its got no real power. replaced pre cat o2 sensor and still no real luck. before it noticed it ran rougher idle but new o2 seemed to almost fix it. it had a little bit of a miss that you could hear. no ses. cpi regulator is about 8 months old. still getting really good mpg. about 21-24 hwy so it cant be the cpi. new plugs, cap rotor and wires about 2 months old. it was doing this before that as well. at highway speed the truck runs fine like nothings wrong. just when driving it around town. also while the trucks idling it seems to run a little lean. drivings not to bad but does at times. fuel filter is about 3 years old and 30,000 miles. any ideas?