I just bought a 99 Blazer to pull my boat with and am having some issues. When I pull my boat under a lot of throttle I get a shutter. I have noticed even without the boat if I full throttle it I get a little shutter. I changed the plugs and checked resistance on the plug wires, they all checked out good. I am wondering if I should do a transmission filter change and fluid change. What do you all think about this?

*Merging Posts*

Oh I forgot to add that the blazer has 109k miles

If you have no records of a transmission service being completed, that probably would not be a bad idea. I do not believe this to be your problem though. Sounds more like you need a tune up consisting of wires, cap, and rotor on top of the new plugs you put in (hopefully they were not Bosch).

Wires can ohm out as good, but still leak spark from the insulation. I would take an old spray bottle full of water and mist down the engine while running in the dark. If you see sparks jumping from the wires, replace them.

Also, you should remove the cap and check the condition of the terminals on the inside of the cap as well as the condition of the rotor.