If the Plugs/Cap/Rotor/Ignition wires/Coil have a pile of miles on them, it wouldn't hurt to upgrade them (I used the stock NGK plugs BPR5EY I beleive they are, Accel 8.8MM Ignition Wires, MSD High Vibration coil and the OEM cap/rotor and startup/takeoff was alot nicer, and obvisouly much cleaner combustion. I don't know too much about these particular carb vehicles. depending on how many miles are on the truck your catalytic could be plugged up and possibly your mixture is off a little bit. Obviously try the cheapest route first, more then likely that will cure your problem