Hotrod Lincoln asked about the governor, I was thinking that is a possibility unrelated to the electrical work. If the original governor is still being used, and the speedo and 2 speed are found to be working correctly, it could easily be a problem with the governor. Adjustments, cleaning and lubrication, and possibly the need for a new governor spring. Years ago while I was working for the local Budweiser distributor, I had a city route tractor that would lose throttle accuracy. We were using 366 and 427 gas motors at that time, Holley 4 bbl with governors. A small spring inside the carb mounted section actually pulls the throttle open when the governor allows it, I found that spring would lose it's tension when the engine was worked all day and good and warm. New spring from the Chevy dealer put it back in business. My '57 2 ton 283 2 bbl uses the same technology and spring, I had to replace that spring 2 years ago due to losing power.
