Lately I've been noticing that when coming to a stop, my speedo is lagging a lot. When I come to a stop, it will show 2mph for a second, then 1mph for a second and then back to 0.

I do have a ricks yellow jacket speedo corrector installed because I have 4.77 gears but I never noticed the lag is so bad until lately. Also, I know it's calibrated to the correct speed because I used a GPS speedo to compare it to and it was 99% on the dot.

What could cause the speedo to lag?

 

Loose ground wire on the back of the cylinder head will cause the speedometer to operate erratically. So will any poor yellow box connections.

 

I have a feeling it must be the yellow jacket then because it worked fine before I installed it onto my car. What should I start with? The connections are tight and it's only been in my car for 2 months or less.