85 2m4 engine problem

85 2m4 180K miles runs good cold after it warms up it looses power on
low rpms. The car when i say it looses power it like stumbles or bucks
mainly noticable uhen the rpm's are low like running on the highway
climbing a hill at 60 65 mph it will buck if I down shift to 4th
getting rpms up it will climb the hill easier Also when I am first
getting onto the highway it will start to buck if I try to accelerate
to quickly. 

I replaced the O2 sensor as it had a code and I replaced the plugs,
cap & rotor and one plug wire as it was 18K ohms the rest are around
2K. swaped the MAP sensor and replaced the TPS as well.
I replaced some of the more older looking airline tubes as well.
There are no codes at this point.
Any help would be great as its driving me crazy.
Hank