I wouldn't trust electrical tape to handle the voltages of a spark wire (~30,000 volts). If one wire is old enough to be worn out, you can't say for sure what the condition of the wire under the insulation is. Do yourself and your car a favor and get a new set. Also make sure your #6 wire isn't touching the nearby O2 sensor wire -- that could cause interference.
You indeed have a rev limiter at 4000 RPM, when going 15 MPH or less. To get around it, shift into neutral when you're moving, and it'll hit the redline limiter at ~6000 RPM. (Do this when safe -- don't kill yourself or others.)
Finally, 24 MPG on a 1997 SE? I only get that when I drive almost all highway miles. What'* your secret?
2007 Pontiac G5
1999 Pontiac Grand Prix GT - Stock engine ate transmission.
1997 Pontiac Bonneville SE - Cammed engine ate transmission.