90 Chevy K3500 454 bucking/service engine soon light

I have a truck that was purchased a few months ago. It is a 1990 Chevy K3500 with 454, manual 4 speed, 4x4. This truck ran fine, although it always takes about 2-3 seconds of continous cranking before it starts. Once started it runs fine although the engine shakes a bit at idle.

I use this truck as a plow truck, and it has worked well up until a few days ago. It has developed a bucking/loss of power when under load at part throttle. Sometimes the Service Engine Soon light comes on breifly, then turns off. Easing off the gas makes it go away, as well as accelerating slowly. Trying to accelerate more quickly causes the bucking. I am suspecting an ignition timing or lack of advance issue, but would appreciate any other possibilities. The previous owner purchased it new, and was religious with its maintenance, the truck looked brand new. It has about 150,000 miles, all 5th wheel towing miles. It spent the last few years only being used to put their boat in the water, so it was driven less than 50 miles a year the last few years.

These trucks are very succeptible to distributor cap corrosion, but the bucking your describing, coupled with the 2 to 3 seconds of cranking time would lead me more towards a plugged fuel filter or weak fuel pump. Since it's only 8 bucks and 10 minutes I'd switch the filter first.

Pulled cap and rotor, very corroded. I cleaned them and reinstalled, truck runs much much better. Probably will replace soon, I just wanted to make sure before spending the loot. Thanks...

Any codes? My guess is the 0-2 sensor is going bad. That happened on a 89 model 350 I had once.