I have a 98 Jimmy with 98k original miles. It was misfiring constantly so the engine was torn down and there is a list of parts to replace. The way I look at it, I already have the engine pulled apart down to the block and I am replacing alot of parts, why not upgrade them and a few other parts. Here are the parts that are needing replaced:

Camshaft Bearings
Timing Chain Set
Std size ring set
Oil Pump
Crankshaft Bearings (waiting on size requirements)
heads are pretty bad
intake valves are almost all bad

I have read somewhere that there is an awesome camshaft you can install that will give you a massive HP boost. But idk if that was an older engine style or what.
We are also trying to avoid doing any kind of computer reprogramming.

Thanks in advance,

 

since you are doing cam bearings, id do the cam also. A 270° cam will boost performance and still idle at stoplights. When you get to 280° you'll need a higher stall converter. Look into 1.6 rockers. Any taller and you'll spend big bucks on valve covers to clear them. I hope this helps