Been doing the preventative maintenance service game for about 12 years now; here's the skinny on flushes
.
If your fliud is not broken down (thinned out and/or discolored) and you are at the recommended service interval, flushing the system is good for it. Don't be scared off by the fact that it has 100k on the fluid, the same fluid was recommmended every 30k until they started making transmissions that ran cooler than NASA rockets. Cooler running transmissions make for longer lasting fluids (hence why GM leads the field as one of only a few manufacturers that have a 100k interval)
If the fluid
is broken down, then pan drop, replace filter, refill, run for 5k, rinse and repeat.
Theory behind this (and I've seen it happen). If your fluid is in good shape and you are at the rec. interval, it is good to perform the service, the interval is in place to keep your fluid from getting bad.
If you have gone past the rec. interval, or you fluid is in poor condition, flushing the system will
shock the gearbox. Over time, your transmission adjust to the fluid as it slowly breaks down, similar to how most people dont realize their shocks are worn out because they have adjusted to them as they have worn out. If you flush out your thinned out fluid with completely new fluid, you are going to shock the transmission because it doesnt know how to perform with the good fluid, causing problems. Instead of changing all the fluid, do 1/3 of it, and let the transmission
readjust itself as it gets used to the better fluid.
Another thing that I notice on the first post.
I have so far changed the plugs(ac delco, which I will be pulling to re-gap to .040, as I followed the owners manual and went 10 .060), plan on new wires as well.
Maybe Im thinking of a different year/engine, but I thought this engine took irridium spark plugs, which you
do not want to regap.