A few other things for your consideration.
Flat spots in acceleration or deceleration may just be blocked jets. Pull them out, clean them then put them back in.
Mr Rocky is likely correct, but you may be able to get away with a jet clean.
This is what a completely blocked jet looks like, it starves the engine of fuel at certain spots in your acceleration and deceleration.

This could cause lack of power and top speed too, but that could also be a number of other things such as a buggered catalytic converter.
Is the fuel old? Fuel that's more than a few months old can cause issues (unless it's very old it isn't likely to be that, but worth considering).